rtlwifi: btcoex: Add pre- and post- normal LPS function

Normal LPS is decomposed into pre- and post- parts, so we can issue H2C
with TDMA parameters in the "critical section" that dirver can't change
LPS state at the moment.

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