gallium: add TGSI_PROPERTY_FS_BLEND_EQUATION_ADVANCED

For virgl, we don't lower advanced equation to fbfetch
So we need to pass the blend equation info in the TGSI to the host

Signed-off-by: Elie Tournier <elie.tournier@collabora.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5516>
2 files changed