flash/stm32l4x: introduce 'stm32l4x trustzone [enable|disable]' command

flash/stm32l4x: introduce 'stm32l4x trustzone [enable|disable]' command

this command will help to enable/disable or display the TrustZone security,
using the TZEN option bit.

Note: This command works only with devices with TrustZone, eg. STM32L5.
Note: This command will perform an OBL_Launch after modifying the TZEN.

Change-Id: I4aef15bf57d09c1658d37858143d23b1d43de1f0
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/5542
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>