ARM: at91: remove old AT91-specific drivers

GPIO and LED drivers were replaced by generic ones for DT boards. These drivers
were remaining: delete them now. Modifications are also done on the
corresponding header files.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[nicolas.ferre@atmel.com: split patch]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>