ARM: shmobile: koelsch: set .debounce_interval

In R-Car GPIO hardware block, 'chattering removal' feature can be
enabled on GPIO-n-[3:0] pins, but it's not supported on rest of pins
GPIO-n-[31:4].

Set an appropriate debounce interval, instead.  We could confirm that
spurious/unnecessary GPIO interrupts are prevented by this settings.

Based on work for the lager board by Shinya Kuribayashi.

Cc: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>