ASoC: msm8974: Add external amplifier on lineout path for Fluid

The msm8974 Fluid has external amplifier which is controlled by GPIO for
emitting of ultrasound on the lineout path.
Get the GPIO from device tree and enable external amplifier to enable
amplifier on the lineout path.

Change-Id: Ie4b912ee1bbd491f43513a33fda3487c808c9358
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>