i965/miptree: Remove the width/height < 32768 restrictions

i965/miptree: Remove the width/height < 32768 restrictions

These restrictions existed because intel_miptree_blit couldn't handle
surfaces bigger than 32k.  How that we're chopping blits up into chunks, it
can handle any size we throw at it so we can get rid of this restriction.
This improves the terrain tests in synmark by 25-30% on my Sky Lake gt3.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reported-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>