msm: camera: util: Add support for option clk

Camera devices can have clocks which need not be turned ON
by default and only in some usecases. These are represented in
DT by clock-names-option and clocks-option. Add APIs for the
devices to get references to these clocks and then enable them
using the existing clk_enable API.

Change-Id: I12812e9cbe754e37d2c9a074a91ee1d02c323352
Signed-off-by: Harsh Shah <harshs@codeaurora.org>