rtlwifi: btcoex: Add enum DM_INFO for btcoex to query dm's counters

btcoex uses dm's counters to check the environment is noisy or not. If it
is clean, btcoex set more time slots to WiFi so that it can transmit as
soon as possible. That will save time, and BT will have more time slots
after WiFi traffic is complete.

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>