msm: vidc: Mark certain decoder controls as read-only

Several of the controls cannot be modified.  Today attempting to set
these controls is a silent NOOP.  This commit causes clients attempting
to modify these controls to fail with -EPERM.

Change-Id: I175e8e1372dc60bf6f0e8527a20f5959d3728f3c
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>