msm: camera: core: Multiple fixes in NRT flush

Removes potential double add to context free list.
Clears request from context lists immediately in
case of flush specific request. Clears context
active list after drivers complete flush in case
of flush context.

Change-Id: I5a1edd1f5eaf7787d81f90a9afe7c3bf6c01e57d
Signed-off-by: Venkat Chinta <vchinta@codeaurora.org>
Signed-off-by: Pavan Kumar Chilamkurthi <pchilamk@codeaurora.org>