Minor tweaks for 3m4m test drivers.

Details:
- Changed gemm_kc blocksizes to be reduced by two-thirds instead of
  half.
- Changed 3m4m/test_gemm.c driver to divide by 3 instead of 2 when
  computing the fixed k dimension.
- Fixed runme.sh so that it would use multiple threads for s/dgemm
  cases.