[WATCHDOG] Enable watchdog timer on GE Fanuc's SBC610

Support for the FPGA based watchdog timer on GE Fanuc's SBC610.

This patch enables one of the watchdog timers found on the SBC610. There are
two identical watchdog timers at different offsets in the above mentioned
boards, however the current driver is only capable of supporting one of them.

The watchdog timers are also capable of generating interrupts at a
user-configurable threshold, though support for this operation is currently
not supported by the driver.

Signed-off-by: Martyn Welch <martyn.welch@gefanuc.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>