rtw89: add C2H handle of BCN_CNT

This C2H notify driver the beacon count we send out. We don't handle the
content for now, so add a dummy handler to avoid messages, like
  rtw89_pci 0000:03:00.0: c2h class 0 func 3 not support
  C2H: 00000000: 01 03 01 3f 0f 00 00 00 80 0a 00 00 00 00 a0
  rtw89_pci 0000:03:00.0: c2h class 0 func 3 not support
  C2H: 00000000: 01 03 01 40 0f 00 00 00 00 03 20 00 00 00 a5

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220107034239.22002-5-pkshih@realtek.com