realtek: eth: simplify mac port control access

realtek: eth: simplify mac port control access

The ethernet driver uses an indirection for access to the MAC_PORT_CTRL
register (aka. MAC_L2_PORT_CTRL on RTL93xx). It defines the base address
and adds up the cpu port offset. This is not needed as the driver does
not handle the non-cpu ports. Use direct register access instead and
avoid register confusion by always using the "_L2_" naming.

While we are here:

- Drop the functions and use defines instead
- Add CPU port defines for better readability

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/21691
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>