twl4030_keypad cleanup

Start cleaning up the twl4030 keypad driver to become more
suitable for mainline.

 - Remove false OMAP dependencies:  names, <mach/keypad.h>, Kconfig
 - We don't need a miniature header file
 - Add missing input_sync()
 - Fix section annotations
 - Fix probe() error cleanup
 - Streamline i/o calls
 - Remove needless mutex; maintain key state only via irqs
 - Remove unneeded headers
 - Use "unsigned" for things that can't be negative

The driver should also be renamed as "twl4030_keypad.c"; that will
be a different patch.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Reviewed-by: Trilok Soni <soni.trilok@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>