ARM: debug: Enable DEBUG_BCM_5301X for Northstar Plus SoCs

Northstar Plus SoCs (ARCH_BCM_NSP) have the exact same UART location and
properties like the register shift of 0, so make it usable.

Acked-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>