ARM: dts: msm: update min voltage for pmcobalt s5 and s7

PMCOBALT S5 is an always on regulator that sources the internal
infrastructure for XO. It's minimum operating voltage is 1904 mV.
PMCOBALT S7 has a 900 mV minimum operating voltage.
Update the minimum voltage for PMCOBALT S5 and S7.

Change-Id: I4ec609b45f5313d7c19ff6201742b0c5daf54174
Signed-off-by: Nicholas Troast <ntroast@codeaurora.org>