This is necessary when the vbios image is not directly accessible via
the rom BAR or legacy vga location.
Reviewed-by: NJammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NMonk Liu <monk.liu@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>