Added CAN API for STM32L4xx family

* STM32L4xx family have only one CAN bus

Change-Id: I95dcffac2176dba6d89850e24ba9561c11319f00

Author: BartSX

hal/targets/hal/TARGET_STM/TARGET_STM32L4/PeripheralPins.h

@@ -65,4 +65,9 @@ extern const PinMap PinMap_SPI_MISO[];
 extern const PinMap PinMap_SPI_SCLK[];
 extern const PinMap PinMap_SPI_SSEL[];
 
+//*** CAN ***
+
+extern const PinMap PinMap_CAN_RD[];
+extern const PinMap PinMap_CAN_TD[];
+
 #endif