wifi: rtw89: phy: support DIG per PHY

DIG standing for dynamic initial gain is to define RX coverage. Adjust this
value dynamically to gain good RX performance.

Use PHY context to extend DIG algorithm to support two PHY.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250117072828.16728-5-pkshih@realtek.com