intel/isl: Allow valign2 for texture-only Y-tiled surfaces on gen7
intel/isl: Allow valign2 for texture-only Y-tiled surfaces on gen7

The restriction that Y-tiled surfaces must have valign == 4 only aplies to
render targets but we were applying it universally.  This causes problems
if ISL_FORMAT_R32G32B32_FLOAT is used because it requires valign == 2; this
should be okay because you can't render to that format.

Signed-off-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Reviewed-by: Chad Versace <4b94d436ff8c93527a96d251ac64b06311506efe@chromium.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler