ARM: dts: msm: Add minimum CX vote for GPU CX GDSC on Lito

Add the vdd_parent supply for GPU CX GDSC to ensure minimal CX vote when
the GDSCR is enabled, thus this would ensure the CX cannot go
lower/collapse when GPU CX GDSCR is enabled.

Change-Id: I0ea71211191f0623a59e6c09ffceac2a7f7a8f01