drm: msm: update cpu1 hotplug by using cpu_device node

update cpu1 hotplug by using its device structure
online callback. This is to ensure, sysfs entry for
cpu1 reflects the online status correctly.

Change-Id: Idc77a1074ca030ca826eb1a817b1ab7795e8548c
Signed-off-by: Vivek Kumar <vivekuma@codeaurora.org>