[WATCHDOG] ep93xx: implemented watchdog timer driver for TS-72xx SBCs

Technologic Systems TS-72xx SBCs have external glue logic
CPLD which includes watchdog timer. This driver implements
kernel support for that.

Signed-off-by: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>