crc32.h: Add a definition for CRC-32 size

CRC-32 size definition will be useful for TLS purposes, but
it is not specific enough to put it in nvmf or nvme_tcp headers.
Therefore, place it in header `crc32.h`.

Change-Id: I45bb4de3d275f22f11f9308d92f159d692c9f61b
Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/17826


Community-CI: Mellanox Build Bot
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>