drm/msm/sde: avoid rot prog fetch config on secondary display

During resolution switch and hpd use-case on dp, vsync timeout
is coming. This is because of rot programmable fetch getting
programmed for non primary encoder. Fix this by adding a check
for primary encoder.

Change-Id: If1e3c3b5754c7f4ed52b15f0d3dd5eaad5fad2b2
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>