i965: Defer input lowering for tessellation stages until specialization.

i965: Defer input lowering for tessellation stages until specialization.

With tessellation shaders and SSO, we won't be able to always decide on
VUE map layouts at LinkProgram time.  Unfortunately, we have to delay it
until shader specialization time.

However, uniform lowering cannot be deferred - brw_codegen_*_prog()
reads nir->num_uniforms.  Fortunately, we don't need to defer it -
uniform, system value, atomic, and sampler lowering can safely stay
where it is.  This patch moves those to brw_lower_nir()'s only caller,
renames brw_lower_nir() to brw_nir_lower_io(), and introduces calls
to that.

For non-tessellation stages, I chose to call brw_nir_lower_io() from
brw_create_nir(), so it's still done at the same time.  There's no
need to defer it, and doing it at LinkProgram time is nice.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>