vexpress64: Juno: Add initialisation code for Juno R1 PCIe host bridge.

Juno R1 has an XpressRICH3 PCIe host bridge that needs to be initialised
in order for the Linux kernel to be able to enumerate the bus. Add
support code here that enables the host bridge, trains the links and
sets up the Address Translation Tables.

Signed-off-by: Liviu Dudau <Liviu.Dudau@foss.arm.com>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
[trini: Always declare vexpress64_pcie_init and continue handling logic
inside the function]
Signed-off-by: Tom Rini <trini@konsulko.com>