[WIP] Update SDK to 2.0.0 (#2304)

[marvelousNinja]

For those who will struggle to run this with PlatformIO (I have version 2.11.1), here is a guide:

1. Copy and replace files from this repo to ~/.platformio/packages/framework-arduinoespressif/.
2. Add some missing build flags to your platformio.ini (bluntly stolen from Compilation error with Ardino/master, lack of newlibc maybe? #2263):

build_flags = -I$PLATFORMFW_DIR/tools/sdk/libc/xtensa-lx106-elf/include -L$PLATFORMFW_DIR/tools/sdk/libc/xtensa-lx106-elf/lib -lc

3. Make some manual modifications to linker scripts. Simple copy & replace won't do since target file has some PlatformIO specific changes. You need to modify this file:
   ~/.platformio/.platformio/packages/ldscripts/esp8266.flash.common.ld.

It should comply with changes from files in this repo:

• Arduino/tools/sdk/ld/eagle.app.v6.common.ld
• Arduino/tools/sdk/ld/eagle.rom.addr.v6.ld

In my case, I had to apply the following changes:

...

*.pioenvs/*/src/*.o(EXCLUDE_FILE (umm_malloc.o) .literal*, \
EXCLUDE_FILE (umm_malloc.o) .text*)
*libc.a:(.literal .text .literal.* .text.*)          /* <======= add this line */
*libm.a:(.literal .text .literal.* .text.*)
*libgcc.a:_umoddi3.o(.literal .text)
*libgcc.a:_udivdi3.o(.literal .text)
*libsmartconfig.a:(.literal .text .literal.* .text.*)
*libmbedtls.a:(.literal .text .literal.* .text.*)    /* <======= add this line */
*(.irom0.literal .irom.literal .irom.text.literal .irom0.text .irom.text .irom.text.*)
...

PROVIDE ( SPI_write_enable = 0x4000443c );
PROVIDE ( Wait_SPI_Idle = 0x4000448c );
PROVIDE ( Enable_QMode = 0x400044c0 );               /* <======= add this line */
PROVIDE ( SPIEraseArea = 0x40004b44 );
PROVIDE ( SPIEraseBlock = 0x400049b4 );
...

[codecov-io]

Current coverage is 27.62% (diff: 100%)

Merging #2317 into master will not change coverage

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[marvelousNinja]

@igrr, what are the next steps? Here's something from the top of my head:

1. Update 'Upgrading SDK' doc with a couple of details. It might speed up SDK upgrades in the future.
2. Update SDK version file, release notes & stuff.
3. There are some new static library files in the diff (and some of them were in the previous SDK releases too). They probably should be deleted: libdriver.a, libgcc.a and liblwip_536.a (this one is new).
4. Flash layout issue you've mentioned. To be honest, I'm not sure where to begin. I'm not a C++ expert by any means, but I find this segfaultfest a bit refreshing.

[igrr]

Flash layout needs to be fixed:

• reduce irom0_0_seg length by 4096 bytes for all flash layouts, except 4m1m (see tools/sdk/ld/eagle.flash.*.ld). For 4m1m layout, there is a 2 megabyte hole between the end of irom0_0_seg and SPIFFS, so lowering irom0_0_seg size is not needed.
• add PROVIDE( _RFCAL_start = 0x40xxxxxx ); with the address of this new 4k sector. This sector will be at the end of irom0_0_seg, 4096 bytes lower than _SPIFFS_start). Adding something like PROVIDE( _RFCAL_start = _SPIFFS_start - 0x1000 ); is also a good option to reduce the number of hardcoded constants.
• add PROVIDE( _OTA_end = _RFCAL_start ); to make the end of code segment more explicit.
• cores/esp8266/Updater.cpp uses _SPIFFS_start as the end address of code segment. Replace that with _OTA_end. Same probably happens in cores/esp8266/Esp.cpp. Also grep other source files in cores/ and libraries/ folder and check if _SPIFFS_start is used outside of the actual SPIFFS implementation and fix if necessary.
• use &_RFCAL_start in user_rf_cal_sector_set (calculate sector number by subtracting 0x40200000 and dividing by 0x1000).
• test if OTA and SPIFFS functions work with each flash layout after these changes (probably the hardest part).

Other things to do:

• update LwIP source code (tools/sdk/lwip) and do make install in tools/sdk/lwip/src.
• revert changes to c_types.h (it should work okay without redefining stuff from stdint.h)

[igrr]

Opened #2440 which addresses points outlined above.