net: stmmac: rk: rk3328: gmac2phy only supports RMII

net: stmmac: rk: rk3328: gmac2phy only supports RMII

As detailed in a previous commit ("net: stmmac: rk: convert rk3328 to
use bsp_priv->id") rk3328 gmac2phy only supports RMII, whereas gmac2io
supports both RMII and RGMII. Clear supports_rgmii for gmac2phy.

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 gmac2io,rk3568,rk3588
Link: https://patch.msgid.link/E1vnYxw-00000007hox-0DqH@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>