ARM: dts: BCM5301X: Specify USB ports for each controller

Northstar has 3 controllers: OHCI and EHCI (each with 2 ports) and XHCI
(with just 1 port). Describe them in the DT. In future this will allow
to reference them as trigger sources.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>