intel: Clarify intel_screen_make_configs

intel: Clarify intel_screen_make_configs

This function felt sloppy, so this patch cleans it up a little bit.

- Rename `color` to `i`. It is not a color value, only an iterator int.
- Move `depth_bits[0] = 0` into the non-accum loop because that is where
  it used. The accum loop later overwrites depth_bits[0].
- Rename `depth_factor` to `num_depth_stencil_bits`.
- Redefine `msaa_samples_array` as static const because it is never
  modified. Rename to `singlesample_samples`.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>