Prepare BSP for Internal Flash filesystem (arduino#316)

* update upload tool for adafruit_proxlighttrinkey_m0 to bossac18

* fake SPI Interface so we could compile with SdFat

Author: hathach

boards.txt

@@ -581,7 +581,7 @@ adafruit_proxlighttrinkey_m0.vid.1=0x239A
 adafruit_proxlighttrinkey_m0.pid.1=0x0103
 adafruit_proxlighttrinkey_m0.vid.1=0x239A
 adafruit_proxlighttrinkey_m0.pid.1=0x8104
-adafruit_proxlighttrinkey_m0.upload.tool=bossac
+adafruit_proxlighttrinkey_m0.upload.tool=bossac18
 adafruit_proxlighttrinkey_m0.upload.protocol=sam-ba
 adafruit_proxlighttrinkey_m0.upload.maximum_size=262144
 adafruit_proxlighttrinkey_m0.upload.offset=0x2000

variants/proxlighttrinkey_m0/variant.cpp

@@ -41,7 +41,7 @@ const PinDescription g_APinDescription[]=
   // Interrupt D6
   { PORTA,  0, PIO_DIGITAL, (PIN_ATTR_DIGITAL|PIN_ATTR_PWM|PIN_ATTR_TIMER), No_ADC_Channel,  PWM2_CH0, TCC2_CH0, EXTERNAL_INT_0 },
 
-  // USB pins
+  // USB pins D7, D8, D9
   { PORTA, 28, PIO_COM, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, // USB Host enable
   { PORTA, 24, PIO_COM, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, // USB/DM
   { PORTA, 25, PIO_COM, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, // USB/DP

variants/proxlighttrinkey_m0/variant.h

@@ -103,8 +103,21 @@ static const uint8_t A2  = PIN_A2;
 
 /*
  * SPI Interfaces
+ * Fake SPI Interface just so we can compile
  */
-#define SPI_INTERFACES_COUNT 0
+#define SPI_INTERFACES_COUNT 1
+
+#define PIN_SPI_MISO         PIN_A0
+#define PIN_SPI_MOSI         PIN_A0
+#define PIN_SPI_SCK          PIN_A0
+#define PERIPH_SPI           sercom0
+#define PAD_SPI_TX           SPI_PAD_0_SCK_1
+#define PAD_SPI_RX           SERCOM_RX_PAD_0
+
+static const uint8_t SS	  = PIN_A0;
+static const uint8_t MOSI = PIN_SPI_MOSI;
+static const uint8_t MISO = PIN_SPI_MISO;
+static const uint8_t SCK  = PIN_SPI_SCK;
 
 /*
  * Wire Interfaces