hw/i386/amd_iommu: Rename SysBus specific functions as amdvi_sysbus_X()

Various functions are SysBus specific. Rename them using the
consistent amdvi_sysbus_XXX() pattern, to differentiate them
from PCI specific functions (which we'll add in the next
commit).

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210926175648.1649075-3-f4bug@amsat.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>