ARM: mach-shmobile: IRQ driven GPIO key support for Kota2

Now when GPIO IRQs are supported on sh73a0 modify the Kota2
board code to switch from the polled "gpio-keys-polled" driver
to the IRQ driven "gpio-keys" driver.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>