pinctrl: exynos: Add AUDIO pin controller for exynos7

Audio IPs on Exynos7 require gpios available in AUDIO
pin controller block. So adding the AUDIO pinctrl support.

Signed-off-by: Padmavathi Venna <padma.v@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>