lima/ppir: Add gl_PointCoord handling

Treat gl_PointCoord as a system value and
add the necessary bits for correct codegen.

Signed-off-by: Andreas Baierl <ichgeh@imkreisrum.de>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
6 files changed