wcn36xx: Advertise ieee802.11 VHT flags

This patch adds ieee802.11 VHT flags for the wcn3680b.

- RX_STBC1
- SU Beamformee
- MU Beamformee
- VHT80 SGI
- Single spatial stream

RX LDPC is declared as supported in the datasheet but not enabled at this
time.

After this patch is applied an AP should see the wcn3680 as an 802.11ac
capable device.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200910150822.2179261-5-bryan.odonoghue@linaro.org