For now, only mark the 4x8BitPacked variants as accelerated.
Applications are unlikely to use the "add with saturate" opcodes from
VK_INTEL_shader_integer_functions2, so, technically, all of the
AccumulatingSaturating variants "[provide] a performance advantage over
user-provided code composed from elementary instructions..." on all
Intel platforms. If we encounter an application that cares, we can do
things differently then. Ditto for the non-packed 8Bit, 4-element
vector variants.
v2: Don't memset props as this also zeros sType and pNext. Noticed by
Georg Lehmann in !12617.
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12624>
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