arm: exynos5: fix the number of GPIO groups on bank A

arm: exynos5: fix the number of GPIO groups on bank A

The GPIO bank A has 21 groups :
A0->A3, B0->B3, C0->C4, DO->D1, Y0->Y6

Let's update the constant to match the groups declare in the samsung
GPIO driver, else the GPIO irq driver won't find its babies.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
BUG=none
TEST=on Spring, try to get GPF0[0] as an interrupt.

Change-Id: I44396611d9da618dfe2a739892be4f0924a6f8cf
Reviewed-on: https://gerrit.chromium.org/gerrit/50710
Reviewed-by: Jeremy Thorpe <jeremyt@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>