update virtio_mmio.h

At the time we pulled in virtio_mmio.h from the kernel tree (commit
a08bb43a "kvmtool: Copy Linux' up-to-date virtio headers"), this was
not an official UAPI header file, so wasn't stable and was not shipped
with distributions.
This has changed with Linux commit 51be7a9a261c ("virtio_mmio: expose
header to userspace"), so we can now use that file officially.
However before that the name of some symbols have changed, so we have to
adjust their usage in our source.

This pulls in virtio_mmio.h from Linux v5.18.0.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Link: https://lore.kernel.org/r/20220524150611.523910-2-andre.przywara@arm.com


Signed-off-by: Will Deacon <will@kernel.org>