Invalid for now, but used by vkd3d-proton, where the use case is to convert
a result matrix to lower precision, followed by a store.
For 16bit accumulation matrices, GFX11 only uses 16bits per 32bit register.
RADV's coop matrix code pads the unused space with undefs and uses a vector
with twice as many elements as the matrix length. Extending that to 8bit by
leaving 24 bits unused is unnecessary as these matrices as there
is no hw unit that requires it. And in wave32, it would also result in
vectors larger than NIR's limit.
So tightly pack 8bit matrices without any undef padding.
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34382>
6d2190300a