net: stmmac: rk: combine rv1126 set_*_speed() methods

Just like rk3568, there is no need to have separate RGMII and RMII
methods to set clk_mac_speed() as rgmii_clock() can be used to return
the clock rate for both RGMII and RMII interface modes. Combine these
two methods.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/E1uPk2z-004CFT-0e@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>