mesa: Fix misplaced includes of "main/uniforms.h".

mesa: Fix misplaced includes of "main/uniforms.h".

Several C++ source files include "main/uniforms.h" from an extern "C"
block, which is both unnecessary, because "uniforms.h" already checks
for a C++ compiler and sets the right linkage, and incorrect, because
the header file includes other C++ headers ("glsl_types.h" and
"ir_uniform.h") that are supposed to get C++ linkage.

Reviewed-by: Paul Berry <stereotype441@gmail.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>