msm: display: Limit dynamic fps feature only to MIPI video panels.

As dynamic fps feature is supported only for MIPI video panels,
return -EINVAL if sysfs node is written for panels other than
MIPI video. This change also removes world writable permissions
for sysfs node.

Change-Id: I72260e6032cb8a758b0457c36a808263a981260f
Signed-off-by: Vishnuvardhan Prodduturi <vproddut@codeaurora.org>