Added the missing on-board SPI LSM303C sensor SPI pin definition

to allow programming the sensor via mbed APIs
See issue(#1746)

Author: Helmut Tschemernjak

hal/targets/hal/TARGET_STM/TARGET_STM32L4/TARGET_DISCO_L476VG/PeripheralPins.c

@@ -201,6 +201,7 @@ const PinMap PinMap_SPI_MOSI[] = {
     {PC_3,  SPI_2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI2)},
     {PC_12, SPI_3, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF6_SPI3)},
     {PE_15, SPI_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI1)},
+    {PD_4,  SPI_2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI2)},
     {NC,    NC,    0}
 };
 
@@ -211,6 +212,7 @@ const PinMap PinMap_SPI_MISO[] = {
     {PC_2,  SPI_2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI2)},
     {PC_11, SPI_3, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF6_SPI3)},
     {PE_14, SPI_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI1)},
+    {PD_3,  SPI_2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI2)},
     {NC,    NC,    0}
 };
 
@@ -221,6 +223,7 @@ const PinMap PinMap_SPI_SCLK[] = {
     {PB_13, SPI_2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI2)},
     {PC_10, SPI_3, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF6_SPI3)},
     {PE_13, SPI_1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI1)},
+    {PD_1,  SPI_2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF5_SPI2)},
     {NC,    NC,    0}
 };