OMAP2/3: Initialize gpio debounce register

Some bootloader may initialize debounce register and this will make
dbclk not consist with the debounce register after linux kernel boot
up.

Signed-off-by: janboe <janboe.ye@gmail.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>