The rpi4 has a single nonstandard ECAM. It is broken
into two pieces, the root port registers, and a window
to a single device's config space which can be moved
between devices. Now that we have widened the page
tables/MMIO window, we can create a read/write acces
functions that are called by the SMCCC/PCI API.

As an example platform, the rpi4 single device ECAM
region quirk is pretty straightforward. The assumption
here is that a lower level (uefi) has configured and
initialized the PCI root to match the values we are
using here.
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Change-Id: Ie1ffa8fe9aa1d3c62e6aa84746a949c1009162e0