i965: Enable smooth points when multisampling without point sprites.

i965: Enable smooth points when multisampling without point sprites.

According to the "Point Multisample Rasterization" of the OpenGL
specification (3.0 or later), smooth points are supposed to be enabled
implicitly when multisampling, regardless of the GL_POINT_SMOOTH flag.

However, if GL_POINT_SPRITE is enabled, you get square points no matter
what.  Core contexts always enable point sprites, so this effectively
makes smooth points go away, even in the case of multisampling.

Fixes Piglit's EXT_framebuffer_multisample/point-smooth tests.
(Yes, that's right folks, we actually have Piglit tests for this.)

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>