clk: qcom: Add support for RCG to register for DFS

Dynamic Frequency switch is a feature of clock controller by which request
from peripherals allows automatic switching frequency of input clock
without SW intervention. There are various performance levels associated
with a root clock. When the input performance state changes, the source
clocks and division ratios of the new performance state are loaded on to
RCG via HW and the RCG switches to new clock frequency when the RCG is in
DFS HW enabled mode.

Register the root clock generators(RCG) to switch to use the dfs clock ops
in the cases where DFS is enabled. The clk_round_rate() called by the clock
consumer would invoke the dfs determine clock ops and would read the DFS
performance level registers to identify all the frequencies supported and
update the frequency table. The DFS clock consumers would maintain these
frequency mapping and request the desired performance levels.

Change-Id: Ic22a0963a94026b22913bdbf02b0043bed00ecd7
Signed-off-by: Taniya Das <tdas@codeaurora.org>
[sboyd@kernel.org: Rework registration logic to stop copying, change
recalc_rate() to index directly into the table if possible and fallback
to calculating on the fly with an assumed correct parent]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: David Dai <daidavid1@codeaurora.org>