vfio/igd: Always emulate ASLS (OpRegion) register

vfio/igd: Always emulate ASLS (OpRegion) register

ASLS register represents the base address of OpRegion, and it is
programmed with HPA. In IGD passthrough scenario, it needs to be
reprogrammed with GPA by guest firmware. To prevent guest accessing
wrong memory range, ASLS should always be emulated and cleared.

In GVT-g scenario, emulating ASLS is unnecessary as access is handled
by kvmgt backend [1].

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/i915/gvt/cfg_space.c?h=v6.14#n295

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Reviewed-by: Corvin Köhne <c.koehne@beckhoff.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250505170305.23622-3-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>