isl: don't warn in physical extent calculation for yuv formats

isl: don't warn in physical extent calculation for yuv formats

Those format have correct descriptions already with the exception of
the planar format. In that case we introduce an assert.

This fine because we don't use the planar format in any of our
drivers. There are restrictions on how the addresses of the 2 planes
are relative to one another which make this annoying. The sampler is
also more limited than what we can do with a shader snippet.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2999>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2999>