ASoC: msm: Add support for multiple module unload and load

Check for gpio pin validity before calling
gpio_free. deregister audio notifier so that
while unloading and loading module again, the
old client of notifier is removed cleanly and
new one is added.

CRs-fixed: 2039099
Change-Id: I9a05c5705695d29601d65d1b9cc086515ac480f0
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>