board: freescale: p1_p2_rdb_pc: Delete watchdog max6370 node in load_default mode

CPLD in load_default mode ignores watchdog reset signal. It does not reset
board when watchdog triggers reset signal.

Detect load_default mode by GPIO7 - LOAD_DEFAULT_N and delete watchdog
max6370 node from device to prevent registering driver for non-working
watchdog.

Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>