regulator: cpr3-regulator: add support for LDO maximum headroom

In order to maintain optimum operability of the LDO hardware it is
necessary to impose a maximum voltage difference between the input
and output voltage of the LDOs. Add support for a device tree property
which specifies this maximum voltage difference and enforce it when
configuring the LDO hardware whenever a CPR corner change request
is handled.

Change-Id: Ic58cb16714109b5845d1ed5755a57c62078683b0
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>