regulator: qpnp-regulator: Add support to configure voltage switch mode

Add support for a device tree property, qcom,hpm-enable, which
can be used to configure a voltage switch type regulator to be in
high power mode (HPM).  When a switch is in HPM, over current
protection and soft start are enabled at all times.

The new property can also be used for other types of regulators.
However, this will likely not have the intended result as the
mode of non-voltage switch regulators is controlled at runtime
via regulator framework APIs.

Change-Id: Id3fca7ebbe3eb13b557e6d483494f218989cd64c
CRs-Fixed: 469134
Signed-off-by: David Collins <collinsd@codeaurora.org>