ARM: dts: bcm2711: Enable PCIe controller

This enables bcm2711's PCIe bus, which is hardwired to a VIA
Technologies XHCI USB 3.0 controller.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>