net: stmmac: rk: rk3506, rk3528 and rk3588 have rmii_mode in clock register

net: stmmac: rk: rk3506, rk3528 and rk3588 have rmii_mode in clock register

rk3506, rk3528 and rk3588 have the rmii_mode bit in the clock GRF
register rather than the gmac GRF register. Provide a mask for this
field in the clock register, and convert these SoCs to use this.
Add the necessary code in rk_gmac_powerup() to write this field.

This allows us to get rid of these SoCs set_to_rmii() function. As
such, we need to mark these SoCs as supporting RMII mode.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de> #px30,rk3328,rk3568,rk3588
Link: https://patch.msgid.link/E1vnYyB-00000007hpF-1dwK@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>