regulator: rpm-smd-regulator: add support for level based voting

In the corner based voting scheme the major corners (SVS, NOM, TURBO)
are sequential and there is no room for adding any intermediate
corners in-between these major corners.

Add support for a level based voting mechanism where all the levels
are sparsely distributed between [1 - 65535] leaving enough room
to add intermediate levels as per system requirements.

Change-Id: I4ab78614d90edf020b90de0dad88599859c4f21c
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>