R600: Add texture and sampler data extraction pass. [WIP]

Static sampler_t samplers could be declared in shader. We need to
extract that information for runtime to set up samplers correspondingly.
This is exported as metadata.

Also we need to patch corrent sampler_ids (enumerate them) and texture_ids
in texture sampling intrinsics.
This enumeration is also exported as metadata.

That's what this pass does.

Signed-off-by: Dmitry Cherkassov <dcherkassov@gmail.com>