[WATCHDOG] Add a watchdog driver based on the CS5535/CS5536 MFGPT timers

Add a watchdog timer based on the MFGPT timers in the CS5535/CS5536
companion chips to the AMD Geode GX and LX processors.  Only caveat
is that the BIOS must provide at least a one free timer, and most
do not.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>