meta: Use sampler object in framebuffer blit

meta: Use sampler object in framebuffer blit

Framebuffer blit needs to setup texture sampling with no reference to the
user's texturing state, and a sampler object lets us avoid a bunch of changes
to the user's state setup.

We don't bother caching the sampler object since we're changing parameters in
it based on the filtering option to glBlitFramebuffer().

Fixes piglit GL_ARB_sampler_objects/framebufferblit and rendering in l4d2 (our
setting of srgb decode wasn't being respected due to the user's sampler object
being active).

Signed-off-by: Pauli Nieminen <pauli.nieminen@linux.intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>