glsl: track total amount of uniform locations used

glsl: track total amount of uniform locations used

Linker missed a check for situation where we exceed max amount of
uniform locations with explicit + implicit locations. Patch adds this
check to already existing iteration over uniforms in linker.

Fixes following CTS test:
   ES31-CTS.explicit_uniform_location.uniform-loc-negative-link-max-num-of-locations

v2: use var->type->uniform_locations() (Timothy)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>