phy: cadence: Sierra: Move the link operations from serdes phy to link device

In commit 6f46c744 ("phy: cadence: Sierra: Add a UCLASS_PHY device for
links"), a separate udevice of type UCLASS_PHY was created for each link.
Therefore, move the corresponding link operations under the link device.

Also, change the uclass of sierra phy to UCLASS_MISC as it is no longer the
phy device.

Fixes: 6f46c744 ("phy: cadence: Sierra: Add a UCLASS_PHY device for links")
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Reviewed-by: Georgi Vlaev <g-vlaev@ti.com>