disp: msm: sde: add dsc block check in the encoder

In some targets, dsc disable API is being called even
though there are no dsc blocks available. This change adds
a check for dsc block in the encoder.

Change-Id: I7fb1e85e21847ee59f47624318695208efad88ca
Signed-off-by: Yashwanth <yvulapu@codeaurora.org>