Fix compile error "FlashIAPBlockDevice.h" not found

Bring back includes from previous commit: 0f54d0f

Author: nseidle

platform.txt

@@ -24,7 +24,7 @@ defines.ld={defines.all} "@{build.variant.path}/mbed/.ld-symbols"
 includes.core={includes} "-I{cores.path}/arduino" "-I{cores.path}/arduino/mbed-bridge" "-I{cores.path}/arduino/mbed-bridge/core-api" 
 includes.mbed="@{build.variant.path}/mbed/.includes"
 includes.variant={build.includes}
-includes.extra=
+includes.extra="-I{cores.path}/mbed-os/drivers/"
 includes.all={includes.core} {includes.mbed} {includes.variant} {includes.extra}
 
 # libraries