i965: fix inverted point sprite origin when rendering to FBO

i965: fix inverted point sprite origin when rendering to FBO

When rendering to FBO, rendering is inverted. At the same time, we would
also make sure the point sprite origin is inverted. Or, we will get an
inverted result correspoinding to rendering to the default winsys FBO.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44613

NOTE: This is a candidate for stable release branches.

v2: add the simliar logic to ivb, too (comments from Ian)
    simplify the logic operation (comments from Brian)

v3: pick a better comment from Eric
    use != for the logic instead of ^ (comments from Ian)

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>