Input: omap-keypad: Remove dependencies to mach includes

Remove support for omap2+ as it's no longer needed since
it's using matrix-keypad. This way we can remove depency
to plat and mach headers which is needed for ARM common
zImage support.

Also remove INT_KEYBOARD by using omap_kp->irq.

Note that this patch depends on an earlier patch
"ARM: OMAP: Move gpio.h to include/linux/platform_data".

Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org
Acked-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>