drivers: watchdog: Add TI TPS382x driver

Add support for the TI TPS382x series. The IC has an input pin which
should be toggled by the processor and a output pin which should be
connected to the RESET input of the processor. The timeout is not
configurable.

This device can be used by devices which does not have any internal
hardware watchdog device.

Signed-off-by: Jeppe Odgaard <jeppe.odgaard@prevas.dk>