net: stmmac: ingenic: simplify mac_set_mode() methods

net: stmmac: ingenic: simplify mac_set_mode() methods

x1000, x1600 and x1830 only accept RMII mode. PHY_INTF_SEL_RMII is only
selected with PHY_INTERFACE_MODE_RMII, and PHY_INTF_SEL_RMII has been
validated by the SoC's .valid_phy_intf_sel bitmask. Thus, checking the
interface mode in these functions becomes unnecessary. Remove these.

jz4775 is similar, except for a greater set of PHY_INTF_SEL_x valies.
Also remove the switch statement here.

Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vHHqI-0000000DjrV-3ygL@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>