cnss2: support wakeup using gpio

To support remote wakeup of MSM8996, a GPIO needs
to be configured as a wakeup interrupt source.
WLAN firmware can toggle this pin to wakeup the
Host when wireless wakeup is triggered.

Change-Id: Id13652f262f37649bb35196f21ae1ff90b7a637a
Signed-off-by: Rajasekaran Kalidoss <rkalidos@codeaurora.org>