phy: sparx5-serdes: power down all CMUs by default

All CMUs are powered up initially. This uses needless power. This patch
makes sure all CMUs are powered down by default. This involves
configuring a number reference clock and power-down registers of the
CMU.

Individual CMUs are later powered up, when the serdes lanes are
configured.

Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://lore.kernel.org/r/20230417180335.2787494-5-daniel.machon@microchip.com


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