wifi: mt76: mt7915: add module param to select 5 GHz or 6 GHz on MT7916

wifi: mt76: mt7915: add module param to select 5 GHz or 6 GHz on MT7916

Due to a limitation in available memory, the MT7916 firmware can only
handle either 5 GHz or 6 GHz at a time. It does not support runtime
switching without a full restart.

On older firmware, this accidentally worked to some degree due to missing
checks, but couldn't be supported properly, because it left the 6 GHz
channels uncalibrated.
Newer firmware refuses to start on either band if the passed EEPROM
data indicates support for both.

Deal with this limitation by using a module parameter to specify the
preferred band in case both are supported.

Fixes: b4d093e321bd ("mt76: mt7915: add 6 GHz support")
Cc: stable@vger.kernel.org
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Link: https://patch.msgid.link/20241010083816.51880-1-nbd@nbd.name
Signed-off-by: Felix Fietkau <nbd@nbd.name>