[ARM] 5263/2: [AT91] GPIO buttons as wakeup sources

Allow the various GPIO-connected buttons to be used as wakeup sources.
Also enable the internal GPIO pullup.

Signed-off-by: Sedji Gaouaou <sedji.gaouaou@atmel.com>
Signed-off-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>