watchdog: sunxi: Add A31 watchdog support

This patch adds support for the watchdog hardware found in A31 and
newer SoCs. This new hardware has registers at different offsets, and
the system reset control has been split out of the "mode" register
into a new "configuration" register.

Differences not supported by this driver include separate interrupt
lines for each watchdog, instead of sharing an interrupt line and
registers with the timer block.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>