add arduino mkr1300 (adafruit#66)

Author: sabas1080

boards/mkr1300/board.mk

@@ -0,0 +1,2 @@
+CHIP_FAMILY = samd21
+CHIP_VARIANT = SAMD21G18A

boards/mkr1300/board_config.h

@@ -0,0 +1,15 @@
+#ifndef BOARD_CONFIG_H
+#define BOARD_CONFIG_H
+
+#define VENDOR_NAME "Arduino LLC"
+#define PRODUCT_NAME "Arduino MKR1300"
+#define VOLUME_LABEL "MKR1300"
+
+#define BOARD_ID "SAMD21G18A-MKR1300-v0"
+
+#define USB_VID 0x2341
+#define USB_PID 0x8053
+
+#define LED_PIN PIN_PA20
+
+#endif