rtlwifi: btcoex: Add power_on_setting routine

commit a44709bba70fb9badc44b6a551415b152db13182 upstream.

After mac power-on sequence, wifi will start to work so notify btcoex the
event to configure registers especially related to antenna. This will not
only help to assign antenna but also to yield better user experience.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>