makefiles: add shared sam0 board makefile include

makefiles/boards/sam0.inc.mk

+# set default port depending on operating system
+PORT_LINUX ?= /dev/ttyACM0
+PORT_DARWIN ?= $(firstword $(sort $(wildcard /dev/tty.usbmodem*)))
+
+# setup serial terminal
+include $(RIOTMAKE)/tools/serial.inc.mk
+
+# Add board selector (USB serial) to OpenOCD options if specified.
+# Use /dist/tools/usb-serial/list-ttys.sh to find out serial number.
+#   Usage: SERIAL="ATML..." BOARD=<board> make flash
+ifneq (,$(SERIAL))
+    export OPENOCD_EXTRA_INIT += "-c cmsis_dap_serial $(SERIAL)"
+    SERIAL_TTY = $(firstword $(shell $(RIOTBASE)/dist/tools/usb-serial/find-tty.sh $(SERIAL)))
+    ifeq (,$(SERIAL_TTY))
+        $(error Did not find a device with serial $(SERIAL))
+    endif
+    PORT_LINUX := $(SERIAL_TTY)
+endif
+
+# this board uses openocd
+include $(RIOTMAKE)/tools/openocd.inc.mk