net: phy: dp83867: add w/a for packet errors seen with short cables
Introduce the W/A for packet errors seen with short cables (<1m) between
two DP83867 PHYs.
The W/A recommended by DM requires FFE Equalizer Configuration tuning by
writing value 0x0E81 to DSP_FFE_CFG register (0x012C), surrounded by hard
and soft resets as follows: