msm: camera: Fix the camera init sequence for dual camera

 - Initialize the camera subsystem cleanly for two concurrent
camera sessions without overwriting the data structures for the
older session.
 - Move the initialization of vfe default variables to vfe reset
as vfe reset is called only for the camera running on PIX interface
 - Add a global holder for the axi output mode to be shared
for multiple config commands.
 - Initialize shared gpios for dual session only once.

Change-Id: I80a42f84de800293ae0c620f7299297467e4ce19
Signed-off-by: Nishant Pandit <npandit@codeaurora.org>