tcl/board: add st_nucleo_g4.cfg to cover known STM32G4 NUCLEO boards

tcl/board: add st_nucleo_g4.cfg to cover known STM32G4 NUCLEO boards

known boards are NUCLEO-G431KB, NUCLEO-G431RB and NUCLEO-G474RE

note: this work safely with B-G431B-ESC1, B-G474E-DPOW1,
      STM32G474E-EVAL and STM32G484E-EVAL

Change-Id: I132a97e1816620b182983edc8a4b272b52b9241d
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/5484
Reviewed-by: Andreas Bolsch <hyphen0break@gmail.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins