clk: clock-local2: Support parsing rcg clocks from dt

Root Clock Generators act as both muxes and dividers.
They support half-integer division, and may optionally
support fractional (M/N) division as well.

Change-Id: I32e19815fa3fe9149492dfa7158c84f5653f5864
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>