ARM: dts: msm: change VDD_MMCX minimum voltage level to LowSVS for SDM855

Change the minimum and initial voltage level for the VDD_MMCX
regulator supply (pm855l_s5_level) to LowSVS.  This corresponds
to the minimum operation level (MOL) of hardware blocks powered
by VDD_MMCX.

Change-Id: Ic928f6b5c6c769ef4df4c117dcb6d8eb819ea81a
Signed-off-by: David Collins <collinsd@codeaurora.org>