msm: krait-regulator: Use default parameters from the device tree

Parameters like the LDO headroom, default LDO voltage, retention voltage
and the LDO threshold need to be configurable. Accept these values from
device tree instead of defining them locally. Note that since these
are required properties the dts is also updated along with the driver
code.

While at it, update the code to program defualt LDO voltage and
retention voltage for the kraits at probe time.

Change-Id: I41a503e1861f8b895be79b9f01fca1f8e217f55d
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>