lima: fix viewport clipping

lima: fix viewport clipping

Apparently Mali4x0 doesn't do viewport clipping, so anything rendered beyond viewport
is still rendered. Looks like we need to use scissors to do clipping.

Fixes most of dEQP-GLES2.functional.clipping.*, 6 out of 7 remaining failures
fail on blob as well. Remaining [1] fails on many other gallium drivers.

[1] dEQP-GLES2.functional.clipping.triangle_vertex.clip_three.clip_neg_x_neg_z_and_pos_x_pos_z_and_neg_x_neg_y_pos_z

Suggested-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Qiang Yu <yuq825@gmail.com>
Tested-by: Andreas Baierl <ichgeh@imkreisrum.de>
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>