ASoC: changes to enable boost gpio only for MTP variants

Boost and UART use the same gpio to function. In QRD, boost circuitry
is not present so changes are needed to support UART functionality
on QRD and remove usage of gpio by audio for boost purposes on QRD.

CRs-Fixed: 808165
Change-Id: Id6e52fbaed6b6d6edf46aac03de66438f8bdf6fa
Signed-off-by: Aravind Kumar <akumark@codeaurora.org>