clk: ti: add support for clock latching to mux clocks

clk: ti: add support for clock latching to mux clocks

Latching the clock settings is needed with certain clocks, where
the setting is "cached" in HW before doing the actual re-programming
of the clock source. This patch adds support for clock latching to
the mux clock.

Signed-off-by: Tero Kristo <t-kristo@ti.com>