ARM: dts: BCM5310X: Harmonize xHCI DT nodes name

In accordance with the Generic xHCI bindings the corresponding node
name is suppose to comply with the Generic USB HCD DT schema, which
requires the USB nodes to have the name acceptable by the regexp:
"^usb(@.*)?" . Make sure the "generic-xhci"-compatible nodes are
correctly named.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>