vulkan: fix coopmat shader generation when cross-compiling (llama/12272)

vulkan: fix coopmat shader generation when cross-compiling (llama/12272)

* vulkan: fix coopmat shader generation when cross-compiling

Previously the status of coopmat{,2} support isn't passed to the
vulkan-shaders-gen project building on the host, which leads to build
failure because of the cross-compiling code expecting coopmat{,2}
shaders that didn't get generated.

Fix this by passing the coopmat{,2} support status to vulkan-shaders
subproject.

Signed-off-by: Icenowy Zheng <redacted>
* Only call coop-mat shaders once

* Fix whitespace

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Signed-off-by: Icenowy Zheng <redacted>
Co-authored-by: bandoti <redacted>