freedreno: Plumb pipe_screen through to irX_tgsi_to_nir.

freedreno: Plumb pipe_screen through to irX_tgsi_to_nir.

This patch makes it possible for freedreno to pass a pipe_screen
to tgsi_to_nir. This will be needed when tgsi_to_nir supports reading
pipe capabilities.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>