brcm63xx: fix lzma loader for BCM6362

BCM6362 and BCM3380 seem to share the same PRID. Disable serial output
for them until we can find a way to tell them apart reliably.

Fixes: 8f3cfe4b ("brcm63xx: lzma-loader: add BCM3380 support")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>