ARM: OMAP: make legacy gpio request/free calls superfluous

Clean up OMAP GPIO request/free functions

 - Rename and declare static OMAP specific GPIO request/free functions
 - Register them into gpiolib as chip-specific hooks
 - Add omap_request_gpio/omap_free_gpio wrappers for existing code not
   converted yet to use gpiolib

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
[ dbrownell@users.sourceforge.net: remove needless check_gpio() calls ]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>