rtw88: coex: Change antenna setting to enhance free-run performance

While the mechanism goes to 2G_free_run or WL5G_BT2G,
set BT to hardware PTA mode to get a more efficiently performance.

Add a flag to indicate antenna switch is supported or not so
that the IC serials which has different antenna structure can
set antenna correctly.

Signed-off-by: Ching-Te Ku <ku920601@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201112031430.4846-8-pkshih@realtek.com