Currently the xilinx_can driver does not support adding a phy like the
"ti,tcan1043" to its devicetree.

This code makes it possible to add such phy, so that the kernel makes
sure that the PHY is in operational state, when the link is set to an
"up" state.
Signed-off-by: Marcel Hellwig <git@cookiesoft.de>
Link: https://lore.kernel.org/r/20230417085204.179268-1-git@cookiesoft.de
[mkl: call phy_power_off() after pm_runtime_put()]
[mkl: remove error message for phy_power_on() failure]
[mkl: update kernel-doc for struct xcan_priv]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>