i965/gen7: Add R8_UINT stencil miptree copy for sampling

i965/gen7: Add R8_UINT stencil miptree copy for sampling

For gen < 8, we can't sample from the stencil buffer, which is
required for the ARB_stencil_texturing extension. We'll make a copy of
the stencil data into a new texture that we can sample using the
R8_UINT surface type.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>