disp: msm: sde: add check for external vote triggered by sysfs node

Changes are made in check for external vote. So that, vote triggered
by change in control node at /sys/class/drm/card0/device/power is
considered to allow gdsc toggle.

Change-Id: I4644cae15930d9f92a7125f4d200f0502d53f0cd
Signed-off-by: Andhavarapu Karthik <kartkart@codeaurora.org>