ARM: dts: msm: Add parent supplies for CX and GX GDSCs for ATOLL

For enabling GPU_CX_GDSC and GPU_GX_GDSC, CX and GFX rails need to
be enabled, so add CX and GFX rails as parents for GDSCs.

Change-Id: I53a2d1a6750e3ec11668abef0198afb29d4fb77c
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>