mt76: mt76x0e: disable 5GHz band for MT7630E

MT7630E hardware does support 5GHz, but we do not properly configure phy
for 5GHz channels. Scanning at this band not only do not show any APs
but also can hang the firmware.

Since vendor reference driver do not support 5GHz we don't know how
properly configure 5GHz channels. So disable this band for MT7630E .

Cc: stable@vger.kernel.org
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>