wifi: mt76: mt7996: select CONFIG_RELAY

Without CONFIG_RELAY, the driver fails to link:

ERROR: modpost: "relay_flush" [drivers/net/wireless/mediatek/mt76/mt7996/mt7996e.ko] undefined!
ERROR: modpost: "relay_switch_subbuf" [drivers/net/wireless/mediatek/mt76/mt7996/mt7996e.ko] undefined!
ERROR: modpost: "relay_open" [drivers/net/wireless/mediatek/mt76/mt7996/mt7996e.ko] undefined!
ERROR: modpost: "relay_reset" [drivers/net/wireless/mediatek/mt76/mt7996/mt7996e.ko] undefined!
ERROR: modpost: "relay_file_operations" [drivers/net/wireless/mediatek/mt76/mt7996/mt7996e.ko] undefined!

The same change was done in mt7915 for the corresponding copy of the code.

Fixes: 98686cd2 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi 7 (802.11be) devices")
See-also: 988845c9 ("mt76: mt7915: add support for passing chip/firmware debug data to user space")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221215163133.4152299-1-arnd@kernel.org