ASoC: msm8x10: Add external PA GPIO enabling code in machine driver

When external PA is used for speaker, it should
be enabled/disabled via GPIO in machine driver
when LINEOUT path is up/down.
Lineout amp is the widget associated with
the external PA enable/disable event.

Change-Id: I6bb276168304b9f537998e438000d42a2d2e0254
Signed-off-by: Walter Yang <yandongy@codeaurora.org>