Add support for openocd on stm32g0 and stm32g4 targets

[erwango]

Is your enhancement proposal related to a problem? Please describe.
stm32g0 and stm32g4 soc support has recently been added on openocd.
openocd support can now be enabled on these targets when flashing debugging

Describe the solution you'd like
Identify openocd SHA1 that enable G4/G0 support.
Enable openocd support on zephyr G4 and G0 supported platforms.
Update board docs
Check everything is fine flash/debug
Request needed change on https://github.com/zephyrproject-rtos/openocd
Close related issues (zephyrproject-rtos/openocd#11)

Additional context
Will avoid need to update pyocd local version to support G4 packages.

[FRASTM]

Actually, I can see the PR zephyrproject-rtos/openocd#11
for G4 but no G0 support

[erwango]

@FRASTM
This is on openocd main repo: http://openocd.zylin.com/#/c/4807/
zephyrproject-rtos/openocd is a fork that needs to be updated

[FRASTM]

To install and use your local openocd:

1. install tools needed to compile OpenOCD
   sudo apt-get install git autoconf libtool make pkg-config libusb-1.0-0 libusb-1.0-0-dev

2. Download the latest source code for OpenOCD with
   git clone http://openocd.zylin.com/openocd

3. Change into the code directory and run the bootstrapper with:
   cd openocd-code
./bootstrap

4. Run make and sudo make install

5. You are now ready to Flash your board with
   west flash --openocd /usr/local/bin/openocd