dev: Use the new ByteOrder param type in VirtIO devices

dev: Use the new ByteOrder param type in VirtIO devices

VirtIO devices currently request their endianness from the System
object. Instead of explicitly querying the system for its endianness,
expose the device's endianness as a param. This param defaults to the
endianness of a parent object using the Parent proxy (in practice the
system).

Change-Id: If4f84ff61f4d064bdd015a881790f5af03de6535
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33296
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabeblack@google.com>