rtw88: coex: update TDMA settings for different beacon interval

Add considering for different WLAN beacon interval in coexistence
mechanism.
Because the WLAN beacon period may be not 100 ms, so it's necessary
to consider any beacon period and set timer according to the interval.

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/20201112031430.4846-2-pkshih@realtek.com