disp: msm: sde: trigger pm_qos vote with encoder idle pc

Commit d46cae01 ("disp: msm: sde: trigger pm_qos vote
with irq enable") moves the pm_qos vote with irq
enable/disable state. Such irq enable/disable call may be
triggered from atomic context and lead to scheduling issues
due to mutex_lock usage in pm_qos APIs. This change moves
the vote with encoder idle pc to allow lock usage with sleep.

Change-Id: I2d22566fbfb5399c5d2d2a4efe882a1928cfbbf8
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>