clk: qcom: Add rcg ops to return floor value closest to the requested rate

clk: qcom: Add rcg ops to return floor value closest to the requested rate

The default behaviour with clk_rcg2_ops is for the
clk_round_rate()/clk_set_rate() to return/set a ceil clock
rate closest to the requested rate by looking up the corresponding
frequency table.
However, we do have some instances (mainly sdcc on various platforms)
of clients expecting a clk_set_rate() to set a floor value instead.
Add a new clk_rcg2_floor_ops to handle this for such specific
rcg instances

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Ritesh Harjani <riteshh@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>