msm: camera: add support for private general ioctl and event

This change adds support for private commands going to the plugin
and private events with payload going to HAL.

Change-Id: Iceb3c3ad1fdc5f45f3bd552b727456ccf54bc006
Signed-off-by: Ankit Premrajka <ankitp@codeaurora.org>
Signed-off-by: Mingcheng Zhu <mingchen@codeaurora.org>