wsi: query the ICD's max dimensions instead of hard-coding them

wsi: query the ICD's max dimensions instead of hard-coding them

anv and radv both happened to already return 2^14 for these, but
querying the ICD is safer and will help if vdreno (or whatever it's
called) doesn't have the same max.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>