radeonsi: add support for ARB_texture_view

radeonsi: add support for ARB_texture_view

All tests pass. We don't need to do much - just set CUBE if the view
target is CUBE or CUBE_ARRAY, otherwise set the resource target.

The reason this can be so simple is that texture instructions
have a greater effect on the target than the sampler view.

Thanks Glenn for the piglit test.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>