Relaxed constraint that KC be multiple of MR, NR.

Details:
- Relaxed a long-held requirement in register blocksizes that required
  the kernel programmer to choose a KC that was divisible by both MR
  and NR. This was very constraining on some architectures that did not
  use register blocksizes that were powers of two. The constraint is
  now enforced only for trmm and trsm, where it is needed, and it is
  now handled by "nudging" kc upward at runtime, if necessary, to be a
  multiple of MR or NR, as needed.
- Defined bli_trmm_determine_kc_[fb]() and bli_trsm_determine_kc_[fb](),
  which determine blocksizes for trmm and trsm, taking special care to
  "nudge" the kc dimension up to a multiple of MR or NR, as needed.
- Changed bli_trmm_blk_var3[fb].c to call bli_trmm_determine_kc_[fb]()
  instead of bli_determine_blocksize_[fb]().
- Added safeguard to bli_align_dim_to_mult() that returns the dimension
  unmodified if the dimension multiple is zero (to avoid division by
  zero).
- Removed cpp guard/check for KC % MR == 0 and KC % NR == 0 from
  bli_kernel_macro_defs.h.
- Whitespace, variable name changes to bli_blocksize.c.
- Removed old commented code from bli_gemm_cntl.c.
Extended newly relaxed KC to hemm, symm.

Details:
- These changes were intended for the previous commit.
- Defined bli_gemm_determine_kc_[fb]() and bli_gemm_determine_kc_[fb](),
  which determine blocksizes for gemm-based operations, taking special
  care to "nudge" the kc dimension up to a multiple of MR or NR for
  hemm and symm operations, as needed.
- Changed bli_gemm_blk_var3f.c to call bli_gemm_determine_kc_f().
  instead of bli_determine_blocksize_f().
- Comment updates to bli_trmm_blocksize.c, bli_trsm_blocksize.c.
Factored common code from blocksize functions.

Details:
- Split bli_determine_blocksize_[fb]() into two functions each, the
  newer ones ending with the _sub suffix. These new sub-functions are
  now called from bli_[gemm|trmm|trsm]_determine_kc_[fb](), which
  eliminates redundant code and will allow any future tweaks to the
  core sub-functions to automatically be inherited by the operation-
  specific versions.