msm: gemini: Make GEMINI a v4l2 subdev.

This has been added to support the
inline JPEG feature. Here the VFE V4L2
subdev sends frames directly to the
Gemini driver. All camera modules like
Sensors, VFE, etc are V4L2 subdevs.

Change-Id: I572afe130ef4f2de441faf1104e688778e0e0ecb
Signed-off-by: Jignesh Mehta <jigneshm@codeaurora.org>
Signed-off-by: Ashwini Rao <ashwinik@codeaurora.org>