vfio/igd: use VFIOConfigMirrorQuirk for mirrored registers

vfio/igd: use VFIOConfigMirrorQuirk for mirrored registers

With the introduction of config_offset field, VFIOConfigMirrorQuirk can
now be used for those mirrored register in igd bar0. This eliminates
the need for the macro intoduced in 1a2623b5c9e7 ("vfio/igd: add macro
for declaring mirrored registers").

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Link: https://lore.kernel.org/r/20250104154219.7209-4-tomitamoeko@gmail.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>