msm: mdss: Return standard errno for error conditions

Replace ENOTSUPP with standard lib error EOPNOTSUPP in order
to update errno. Return EPERM error when VSYNC_ENABLED called
in suspend state in order to reflect the actual state of the
device. if no error returned applications would assume vsync
events are being generated when this is not true.

Change-Id: I72a7347ebecc71376884cf21b7e757f75ba9b40e
Signed-off-by: Ramkumar Radhakrishnan <ramkumar@codeaurora.org>