galileo: Add 'debug' rule

This patch the 'debug' rule to simplify the debugging process. This new
rule runs OpenOCD and gdb with the right parameters. OpenOCD runs in
background and its output will be redirected to a log file in the
application's path called LOG_OPENOCD. Once gdb client is detached,
OpenOCD is terminated.

The 'debug' rule is defined in Makefile.customrules-galileo file (create
by this patch) which is included by the Contiki's buildsystem. So to
debug a Contiki application for Galileo board, run the following command:
$ make TARGET=galileo debug

If you use a gdb front-end, you can define the "GDB" environment variable
and your gdb front-end will be used instead of default gdb. For instance,
if you want to use cgdb front-end, just run the command:
$ make BOARD=galileo debug GDB=cgdb

.gitignore

@@ -113,5 +113,6 @@ platform/galileo/bsp/libc/newlib-2.2.0-1*
 platform/galileo/bsp/grub/src/
 platform/galileo/bsp/grub/bin/
 
-# galileo build artefacts
+# galileo build and debug artefacts
 *.galileo
+LOG_OPENOCD

platform/galileo/Makefile.customrules-galileo

@@ -0,0 +1,8 @@
+GDB ?= gdb
+OPENOCD_SCRIPTS = $(CONTIKI)/platform/galileo/bsp/openocd-scripts
+
+.PHONY: debug
+
+debug: $(CONTIKI_PROJECT).$(TARGET)
+	@openocd -s $(OPENOCD_SCRIPTS) -f debug.cfg &> $(shell pwd)/LOG_OPENOCD &
+	@$(GDB) $< -ex "target remote :3333"

platform/galileo/bsp/openocd-scripts/debug.cfg

@@ -0,0 +1,11 @@
+source [find interface/ftdi/flyswatter2.cfg];
+source [find board/quark_x10xx_board.cfg];
+
+quark_x10xx.cpu configure -event gdb-attach {
+  halt
+}
+
+quark_x10xx.cpu configure -event gdb-detach {
+  resume
+  shutdown
+}