[][kernel][common][eth][Add individual polarity control to the SGMII]

[Description]
Add individual polarity control to the SGMII.
  - pn_swap: Swap TX/RX PN polarity
  - pn_swap_tx: Swap TX PN polarity
  - pn_swap_rx: Swap RX PN polarity

Without this patch, the TX/RX polarity of the SGMII cannot be
controlled individually.

[Release-log]
N/A


Change-Id: I96953f566cd12e57691b54aedfaf475d69912655
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/9094250
2 files changed