disp: sde: hold an extra PM refcount in trusted VM

pm runtime suspend/resume is not supported in trusted vm since
the power domain is controlled by the primary VM. Hold an
extra refcount on the drm device in trusted vm to avoid pm
runtime calls.

Change-Id: I57c22887eb8b11f8ce318479ca36b84cda385d60
Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>