clk: qcom: cpu-8996: Add support to switch below 600Mhz

The CPU clock controller's primary PLL operates on a single VCO range,
between 600MHz and 3GHz. However the CPUs do support OPPs with
frequencies between 300MHz and 600MHz. In order to support running the
CPUs at those frequencies we end up having to lock the PLL at twice the
rate and drive the CPU clk via the PLL/2 output and SMUX.

So for frequencies above 600MHz we follow the following path
 Primary PLL --> PLL_EARLY --> PMUX(1) --> CPU clk
and for frequencies between 300MHz and 600MHz we follow
 Primary PLL --> PLL/2 --> SMUX(1) --> PMUX(0) --> CPU clk

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Ilia Lin <ilialin@codeaurora.org>

Conflicts:
	drivers/clk/qcom/clk-cpu-8996.c