msm: 8909: device OPP registration to manage frequency limits

Support registering OPPs of a device so that the clients
like limits management can request using the OPP layer interface
to get the voltage corners coresponding to the rate of the device.

Change-Id: I32ff2e04fabd25b646570c06911fce0dbb1753cb
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>