pinctrl: exynos: Add spinlocks to irq_mask and irq_unmask

The patch:
  19846950 pinctrl: samsung: Protect bank registers with a spinlock

...added spinlocks to protect many accesses.  However, the irq_mask
and irq_unmask functions still do an unprotected read/modify/write.
Add the spinlock there.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>