ARM: dts: msm: limit VDD_MX requests to 1.2875 V for msm8926-v2

The requirement that VDD_MX be greater than or equal to VDD_APC has been
relaxed on msm8926 v2 in order to allow higher VDD_APC voltages. Because
of this, VDD_MX is limited to a maximum voltage of 1.2875 V by the RPM.
Requests for voltages higher than this limit will cause the system to
crash.

Update the maximum voltage for pm8226_l3 (VDD_MX) regulator nodes to
match the 1.2875 V requirement. Also add a vdd-mx mapping table in the apc
vreg_corner node and change the vdd-mx-vmin selection method to utilize
the table. This ensures that CPR does not attempt to request a voltage
higher than 1.2875 V when operating in the turbo voltage corner.

CRs-Fixed: 607899
Change-Id: Id13b3fcae8cca0848a9e5990978125ba7dcbe572
Signed-off-by: Ke Liu <keliu@codeaurora.org>