softpipe: enable ARB_texture_view

softpipe: enable ARB_texture_view

Some bits were already there for texture views but some were missing.
In particular for cube map views things needed to change a bit.
For simplicity I ended up removing the separate face addr bit (just use
the z bit) - cube arrays didn't use it already, so just follow the same
logic there. (In theory using separate bits could allow for better hash
function but I don't think anyone ever did some measurements of that so
probably not worth the trouble, if we'd reintroduce it we'd certainly
wanted to use the same logic for cube arrays and cube maps.)
Also extend the seamless cube sampling to cube arrays - as there were no
piglit failures before this is apparently untested, but things now generally
work quite the same for cube textures and cube array textures so there
hopefully shouldn't be any trouble...

49 new piglits, 47 pass, 2 fail (both due to fake multisampling).

v2: incorporate Brian's feedback, add sampler view validation,
function rename, formatting fixes.

Reviewed-by: Brian Paul <brianp@vmware.com>