anv: index indirect data buffer with absolute offset

anv: index indirect data buffer with absolute offset

This will help for a follow up change where we will respawn the shader
multiple times in a loop and the base offset will be edited by the
shader itself.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ivan Briano <ivan.briano@intel.com>
Tested-by: Felix DeGrood <felix.j.degrood@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25361>