kvmtool: virtio: pass trapped vcpu to IO accessors

The recent introduction of bi-endianness on arm/arm64 had the
odd effect of breaking virtio-pci support on these platforms, as the
device endian field defaults to being VIRTIO_ENDIAN_HOST, which
is the wrong thing to have on a bi-endian capable architecture.

The fix is to check for the endianness on the ioport path the
same way we do it for mmio, which implies passing the vcpu all
the way down. Patch is a bit ugly, but aligns MMIO and ioport nicely.

Tested on arm64 and x86.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>