[ARM] 5047/2: Support resetting by asserting GPIO pin

This adds support for resetting via assertion of GPIO pin.
This e.g. is used on Sharp Zaurus SL-6000.

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Acked-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>