regulator: spm-regulator: add support for FTS 2.5 type regulators

Add support for QPNP PMIC FTS 2.5 type regulators.  This type of
regulator supports auto mode control, auto phase control, and
three phases enabled at one time.  The FTS 2.5 voltage mapping is
similar to that of existing FTS 2 except for an additional
offset.

Change-Id: I0fa7876ce916f2d039d18a7d89ce7b32c783f68d
Signed-off-by: David Collins <collinsd@codeaurora.org>