ARM: BCM5301X: Enable UART0 on tested devices

There are two possible UARTs so we have (both of) them disabled by
default. Override uart0 status on devices that were verified to use it.
In case of Netgear R6250 also drop an old (and invalid) overwrite. It
doesn't have uart1 connected.

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>