clk: qcom: regmap-phy-mux: Rework the implementation

clk: qcom: regmap-phy-mux: Rework the implementation

The sole reason this hw exists is to let the branch clock downstream of
it keep running, with the PHY disengaged. This is not possible with the
current implementation, as the enabled status is hijacked to mean
"enabled" = "use fast/PHY source" and "disabled" = "use XO source".

This is an issue, since the mux enable state follows that of the child
branch, making the desired "child enabled, MUX @ XO" combination
impossible.

Solve that by implementing ratesetting. Because PHY clock rates may
change at runtime and aren't really deterministic from Linux, assume
ULONG_MAX as "fast clock" and 19.2 MHz as XO. All the branches in
question already set CLK_SET_RATE_PARENT, so everything works out.

Signed-off-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260409-topic-phy_fastclk-v1-1-6b4aaee56b90@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>