ASoC: msm89xx-wcd: add support for speaker boost regulator

In ferrum, external boost is supported which can be set
using gpio-based regulator. Add support to enable and
disable external boost for speaker at powerup and power
down sequence.

Change-Id: I5653c95adb772ee80993b4c377b518a103486816
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>