disp: msm: sde: update uidle ctl register only for master encoder

In case of dual dsi usecase, since both the encoders use
the same CTL path, this change ensures that uidle ctl
settings are updated only by the master encoder.

Change-Id: I7bd75ae0195d34f0c1810403fa5e390fbaa64ed0
Signed-off-by: Yashwanth <quic_yvulapu@quicinc.com>