wifi: rtw89: warn unexpected polling value of XTAL SI

wifi: rtw89: warn unexpected polling value of XTAL SI

XTAL SI is an indirect serial interface to access registers in another
hardware domain. When BT driver initializes UART interface, firmware might
rarely control XTAL SI at the same time causing access racing.

Current is to adjust initialization flow to avoid the racing. To make
the racing visible if it still presents, add a message to address this.

USB adapters might be unplugged suddenly, causing flooding messages. Check
RTW89_FLAG_UNPLUGGED flag to avoid them.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20251223030651.480633-11-pkshih@realtek.com