msm: rpm-regulator-smd: Add LDO voltage corner support

Allow LDO type rpm-regulator-smd devices to utilize voltage
corners.  This is needed to support VDD_CX (LDO 10) on MSM9625
targets.

Change-Id: I004dd9b77c677b07f3fb3e7276e4a047e2884b65
Signed-off-by: David Collins <collinsd@codeaurora.org>