ARM: dts: msm: add optional cpr-regulator supplies for msm8926

CPR regulator needs to choose its vdd_apc supply from multiple optional
power regulators configured in its device tree. Only one of them
will be physically present and CPR will choose its regulator device.

Change-Id: I4365363c55a6d47b202df6e838c54eea1e5fac18
Signed-off-by: Ke Liu <keliu@codeaurora.org>