clk: qcom: clk-regmap-mux-div: Add support for clk rate notifier

There could be a scenario for apcs clock rate change where there is a
requirement to register a clock rate change notifier callback function
so that before configuring apss PLL, RCG source will be switched to safe
source. Add support for the same by adding clock notifier clk_nb.

Change-Id: Icd93b10984d5bf40b57ebe3992ab8f6fa498f4d4
Signed-off-by: Amit Nischal <anischal@codeaurora.org>