ARM: dts: msm: Use voltage floor corner for PM8226 SMPS 1 on msm8226

Add a voltage floor corner regulator interface in the MSM8226
device tree for the PM8226 SMPS 1 regulator (VDD_CX).  This
interface will be used to impose a minimum active voltage corner
in low temperature situations.

Change-Id: Ia83c2062cf1299d9f71954df9dc200c83d0d6a37
Signed-off-by: Jennifer Liu <chihning@codeaurora.org>