Add support for the built in watchdog in AT32AP700X devices.

Tested on AT32AP7000 and ATSTK1000.

Hardware documentation can be found in the AT32AP7000 datasheet.
Signed-off-by: NHans-Christian Egtvedt <hcegtvedt@atmel.com>
Signed-off-by: NHaavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: NWim Van Sebroeck <wim@iguana.be>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>