clk: qcom: clk-rcg2: Introduce a cfg offset for RCGs

The RCG CFG/M/N/D register base could be at a different offset than
the CMD register, so introduce a cfg_offset to identify the offset
with respect to the CMD RCGR register.

Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Anu Ramanathan <anur@codeaurora.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>