boards: nucleo_f412zg: Enable flash and debug with openocd

nucleo_f412zg was missing some files to support flash with
openocd. Fix this lack and update doc.

Signed-off-by: Erwan Gouriou <[email protected]>

Author: erwango

boards/arm/nucleo_f412zg/board.cmake

@@ -0,0 +1 @@
+include(${ZEPHYR_BASE}/boards/common/openocd.board.cmake)

boards/arm/nucleo_f412zg/doc/nucleo412zg.rst

@@ -148,8 +148,7 @@ Programming and Debugging
 *************************
 
 Nucleo F412ZG board includes an ST-LINK/V2-1 embedded debug tool interface.
-However this interface is currently not supported by OpenOCD. You will need
-to use ST tools or an external JTAG probe.
+This interface is supported by the openocd version included in Zephyr SDK.
 
 
 .. _Nucleo F412ZG website:

boards/arm/nucleo_f412zg/support/openocd.cfg

@@ -0,0 +1,12 @@
+source [find board/st_nucleo_f4.cfg]
+
+$_TARGETNAME configure -event gdb-attach {
+        echo "Debugger attaching: halting execution"
+        reset halt
+        gdb_breakpoint_override hard
+}
+
+$_TARGETNAME configure -event gdb-detach {
+        echo "Debugger detaching: resuming execution"
+        resume
+}