Minor cleanups to level-2 _cntl.c files.

Details:
- Changed level-2 _cntl.c files so that the blocksizes for gemv are
  imported and used, rather than blocksizes being declared locally.
- Whitespace changes to gemv_cntl.c and gemm_cntl.c files (as well as
  4m/3m variants).
- Removed test/old/test_blis2.c.
Can now query register blocksizes from blk algs.

Details:
- Added a new field to blksz_t objects that allows one to attach a
  sub-object. Doing this allows us to associate a register blocksize with
  any given cache blocksize. That way, the register blocksize can be
  queried wherever the cache blocksize would normally be accessible
  (e.g. a blocked algorithm).
- Modified bli_gemm_cntl.c (and 4m/3m variants) so that the register
  blocksizes are attached to the cache blocksizes after they are created.