phy: cadence: Sierra: Add support for derived reference clock output

Sierra has derived differential reference clock output which is sourced
after the spread spectrum generation has been added. Add support to drive
derived reference clock out of serdes. Model this derived clock as a
"clock" so that platforms using this can enable it.

Sierra Main LC VCO PLL divider 1 clock is programmed to output 100MHz
clock output.

Signed-off-by: Swapnil Jakhade <sjakhade@cadence.com>
Reviewed-by: Aswath Govindraju <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20211223060137.9252-16-sjakhade@cadence.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>