Details:
- Revamped some parts of commit b6ef84fad1 by adding blocksize extension
fields to the blksz_t object rather than have them as separate structs.
- Updated all packm interfaces/invocations according to above change.
- Generalized bli_determine_blocksize_?() so that edge case optimization
happens if and only if cache blocksizes are created with non-zero
extensions.
- Updated comments in bli_kernel.h files to indicate that the edge case
blocksize extension mechanism is now available for use.
6bfa96f848