ath11k: add ab to TARGET_NUM_VDEVS & co

The next patch changes TARGET_NUM_VDEVS to be dynamic and need access to ab.
Add ab separately to keep the next patch simple.

Compile tested only.

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211209104351.9811-2-kvalo@kernel.org