[ARM] 4602/3: AT91: debugfs interface to view GPIO pin state

This patch adds a debug interface (if CONFIG_DEBUG_FS is selected) to
display the basic configuration and current state of the GPIO pins on
the Atmel AT91 processors.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>