anv: Add a helper for doing buffer copies with nothing but VF and SOL.

anv: Add a helper for doing buffer copies with nothing but VF and SOL.

This method of doing copies has the advantage of touching very little of
the GPU state.  While it does disable all the shader stages, it doesn't
have to blow away binding tables, viewports, scissors, or any other bits of
dynamic state other than VBO 32 which is already reserved.  All of the
state that it does touch is contained within a pipeline anyway so that's
the only thing that has to be dirtied.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>