wcnss: Notify low vbatt level to WCNSS FW

Listen to low vbatt notification from ADC; and send this notification to
WCNSS firmware. Firmware needs to switch to low power mode, when it's a
low batt situation.

CRs-Fixed: 543439
Change-Id: Id78cbde6ca2a5d37ff52ec4feeb7ec04e38b6adb
Signed-off-by: Sameer Thalappil <sameert@codeaurora.org>
3 files changed