mesa/st/glsl_to_tgsi: Split arrays whose elements are only accessed directly

mesa/st/glsl_to_tgsi: Split arrays whose elements are only accessed directly

Array whose elements are only accessed directly are replaced by the
according number of temporary registers. By doing so the otherwise
reserved register range becomes subject to further optimizations like
copy propagation and register merging.

Thanks to the resulting reduced register pressure this patch makes
the piglits

  spec/glsl-1.50/execution -
      variable-indexing/vs-output-array-vec3-index-wr-before-gs
      geometry/max-input-components

pass on r600 (barts) where they would fail before with a "GPR limit exceeded"
error (even with the spilling that was recently added).

v2: * rename method dissolve_arrays to split_arrays
    * unify the tracking and remapping methods for src and dst registers
    * also track access to arrays via reladdr*

v3: * enable this optimization only if the driver requests register merge

v4: * Correct comments
    * Also update inst->resource if it is an array element
      (thanks: Benedikt Schemmer for testing the patches on radeonsi, which
       revealed that I was missing tracking this)

Signed-off-by: Gert Wollny <gw.fossdev@gmail.com>
Acked-by: Dave Airlie <airlied@redhat.com>