realtek: pcs: rtl838x: import SerDes code from DSA/PHY

realtek: pcs: rtl838x: import SerDes code from DSA/PHY

Import functions 'rtl8380_sds_rst', 'rtl8380_sds_power',
'rtl8380_configure_serdes' and 'rtl83xx_config_interface' from DSA and
PHY driver respectively but comment the code for now.

The code needs heavy adjustments to make it compile and work. To make
this as transparent as possible, do that in two stages.

Signed-off-by: Jonas Jelonek <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/20876
Signed-off-by: Hauke Mehrtens <[email protected]>