i965: Support GL_CLAMP natively on Broadwell.

i965: Support GL_CLAMP natively on Broadwell.

The new hardware actually supports this OpenGL 1.x feature natively,
so we can finally drop our shader workarounds.

Not many applications use GL_CLAMP, and most use it unintentionally, but
it's trivial to do right, so we should.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>