ARM: dts: msm: Add the parent supply for CX GDSC for sdm845/670

CX GDSC has a parent supply which is required to be enabled
before turning on CX GDSC; therefore, specify VDD_CX as the
parent supply for CX GDSC.
Also update the min level for VDD_CX regulator.

Change-Id: If770109a03152e98183930289556d6c3cf6ec497
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>