mt76: mt7915: add .set_bitrate_mask() callback

Add runtime configuration for bitrate mask. This update firmware rate
control to add a boundary on top of table to limit the rate selection
for each peer, so when user set bitrates vht-mcs-5 1:9, which actually
means nss = 1 mcs = 0~9. This only applies to data frames as for other
mgmt, mcast, bcast still use legacy rates as it is.

Note that driver does not support GI configuration.

Example:
iw dev wlan0 set bitrates vht-mcs-5 1:9 he-mcs-5 2:7
iw dev wlan0 set bitrates legacy-5 6 he-mcs-5 2:0-11

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>