openocd: add support for Silabs Series-2

Backport the required patches from the upstream to be able to support
Silicon Labs Series-2.

In addition to allow the user to use OpenOCD rather than JLink on
Silicon Labs boards, this patch is required for xiao_mg24 and various
Arduino boards (which don't include JLink hardware).

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>

Author: jerome-pouiller

.gitmodules

@@ -42,4 +42,4 @@
 	url = https://github.com/zephyrproject-rtos/xilinx-qemu.git
 [submodule "openocd"]
 	path = openocd
-	url = https://github.com/zephyrproject-rtos/openocd.git
+	url = https://github.com/jerome-pouiller/openocd.git