tcl/stm32mp15x: freeze watchdog, recover SWD after power cycle

tcl/stm32mp15x: freeze watchdog, recover SWD after power cycle

Freeze the IWDG watchdog when cores are halted to prevent a reset
while debugging.

The PMIC present on some board senses the nsrst and forces a power
cycle to the target. The power cycle causes the SWJ-DP to restart
in JTAG mode. If the debugger is using SWD, the mismatch triggers
an error after the reset command.
Ignore the error detected by 'dap init' and proceed executing the
handler. The error in 'dap init' will force a reconnect during the
following 'dap apid', restoring the SWD functionality.

Change-Id: I04fcda6a5b8a1b080ab4e8890ecd0754d5ed12d9
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6599
Tested-by: jenkins