rtlwifi: btcoex: move bt_type declaration

Routine rtl_get_hwpg_bt_type() is better in halbtcoutsrc.c than in
rtl_btc.c.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>