serial: msm_geni_serial: Vote for shutdown pinctrl during BT off

Currently driver is voting for active/sleep state configuration
during BT disconnect. Since this state contains UART functionality,
GPIO pins remains high which consumes power. This change is added
to vote for the shutdown pinctrl state during BT disconnect and
configure GPIO's in gpio functionality. This is a requirement
from BT SOC team.

Change-Id: I09f7a4a1dbc197c2bfd443a0b546a1ff283134ed
Signed-off-by: Paras Sharma <parashar@codeaurora.org>