soc: arm: Don't touch interrupts in kinetis watchdog init

The early boot watchdog init for kinetis was incorrectly disabling and
reenabling interrupts to preserve timing during the unlock sequence.
However, interrupts are already disabled before this routine executes
and the kernel is not yet ready to enable them when this routine exits.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>