ARM: orion: move custom gpio functions to orion-gpio.h

Move custom orion platforms gpio code to orion-gpio to remove the
dependency on mach/gpio.h.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Cc: Andrew Lunn <andrew@lunn.ch>