clk: clock-local2: Support parsing generic mux type in dt

Represents a mux which may optionally have gating capability.
Add functionality to parse the mux definition in device tree.

Change-Id: I03bbf9c7d4e1b5ddefeee02c588f74e0b7169979
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>