ARM: BCM5301X: Enable earlycon on tested devices

This allows reporting & debugging problems occurring early in the boot
process.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>