mesa: Use uniform interfaces in fixed-function fragment shader code

mesa: Use uniform interfaces in fixed-function fragment shader code

Poking directly at the backing resources works only by luck.  Core
Mesa code should only know about the gl_uniform_storage structure.
Soon other code that looks at samplers will use the gl_uniform_storage
structures instead of the data in the gl_program.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>