wifi: rtw89: mac: separate pre-init code before downloading firmware

wifi: rtw89: mac: separate pre-init code before downloading firmware

Driver needs to initialize registers before downloading firmware, so
move pre-init part (power on) from original rtw89_mac_init(). The
consequence patches will add more pre-init codes before downloading
firmware.

Since rtw89_phy_init_bb_afe() is used by coming RTL8922D, don't change
logic at all for existing chips.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20251114060128.35363-4-pkshih@realtek.com