net: stmmac: rk: introduce flags indicating support for RGMII/RMII

net: stmmac: rk: introduce flags indicating support for RGMII/RMII

Introduce two boolean flags into struct rk_priv_data indicating
whether RGMII and/or RMII is supported for this instance. Use these
to configure the supported_interfaces mask for phylink, validate the
interface mode. Initialise these from equivalent flags in the
rk_gmac_ops or depending on the presence of the ops->set_to_rgmii and
ops->set_to_mii methods. Finally, make ops->set_to_* optional.

This will allow us to get rid of empty set_to_rmii() methods.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de> #px30,rk3328,rk3568,rk3588
Link: https://patch.msgid.link/E1vnYxl-00000007hol-3XiH@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>