nir/linker: update already processed uniforms search for UBOs/SSBOs

nir/linker: update already processed uniforms search for UBOs/SSBOs

Until now, we were using the uniform explicit location to check if the
current nir variable was already processed while adding entries on the
uniform storage. But for UBOs/SSBOs, entries are added too but we lack
a explicit location.

For those we need to rely on the UBO/SSBO binding and the unifor
storage block_index. In that case several uniforms would need to be
updated at once.

v2: (from Timothy review)
   * Improve wording and fix typos of some long comments.
   * Rename update_uniform_storage for mark_stage_as_active

v3: (from cmarcelo review)
   * Fixed some comment typos

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>