msm: rpm-regulator: merge rpm-regulator and rpm-regulator-8960 drivers

Combine rpm-regulator.c and rpm-regulator-8960.c so that only a
single file named rpm-regulator.c contains the RPM regulator
driver logic.  This will initially support both 8660 and 8960.
The data needed to capture the configuration of the RPM regulator
driver on different platforms will be added in platform specific
files.

Change-Id: I57982e73aa7cb30425912b5ff4b90871419e1f8a
Signed-off-by: David Collins <collinsd@codeaurora.org>