ARM: shmobile: r8a7790: link PCI USB devices to USB PHY

Describe the PCI USB devices that are behind the PCI bridges, adding necessary
links to the USB PHY device.

Based on the original work by Ben Dooks <ben.dooks@codethink.co.uk>.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>