ALSA: hda/ca0132 - Create mmio gpio function to make code clearer

This patch adds a new function, ca0132_mmio_gpio_set, to clear up what
is going on with writes to mmio region 0x320.

Signed-off-by: Connor McAdams <conmanx360@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>