ARM: dts: qcom: add VDD_MX and CX subnodes for MMCX dependencies on Lahaina

Add VDD_MX and VDD_CX rpmh-regulator subnodes which are used by
the VDD_MMCX regulator device.  Configure these sub nodes so that
a request for VDD_CX >= minimum operating level is present any
time that VDD_MMCX is enabled.

This ensures that multimedia hardware blocks are not accidentally
reset due to VDD_MMCX being enabled when VDD_CX is not enabled.

Implement the following <child> --> <parent> supply dependencies:

pm8350c_s8_level (MMCX)        --> pm8350_s5_mmcx_sup_level (MxA)
pm8350_s5_mmcx_sup_level (MxA) --> pm8350_s9_mmcx_sup_level (MxC)
pm8350_s9_mmcx_sup_level (MxC) --> pm8350c_s6_mmcx_sup_level (CX)

Note that the final MxC to CX supply dependency only propagates
the enable state of the regulator, not the voltage level.  This
ensures correctness while also minimizing power consumption.

Change-Id: Ib1c7d4fa685e88d62c7e31b1e6a1ae396aed4edb