mesa/glsl: introduce a remap table for uniform locations

mesa/glsl: introduce a remap table for uniform locations

Patch adds a remap table for uniforms that is used to provide a mapping
from application specified uniform location to actual location in the
UniformStorage. Existing UniformLocationBaseScale usage is removed as
table can be used to set sequential values for array uniform elements.

This mapping helps to implement GL_ARB_explicit_uniform_location so that
uniforms locations can be reorganized and handled in a more easy manner.

v2: small fixes + rename parameters for merge and split functions (Ian)
    improve documentation, remove old check for location bounds (Eric)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>