Align with gallium side. When fixed-function blending is not available,
the internal blend shader is used. This is handled by a single ST_TILE
in the blend shader with the current sample ID, which requires sample
shading enablement.
Cc: mesa-stable
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Lars-Ivar Hesselberg Simonsen <lars-ivar.simonsen@arm.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38129>