msm: pil-msa: Move MX regulator voltage to devicetree

Requesting an absolute voltage value for mx will no longer work on
krypton, since different parts may have different maximum mx values. Use
corner voltages instead.

Change-Id: Ie5a43fa1e451944bc3dddfa7b688d842f8746727
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>