ARM: dts: aspeed: Add G4 USB Virtual Hub

This adds the (disabled by default) device node for the
Aspeed virtual hub,a long with clocks and pinmux.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>