crypto: x86/crc32c - simplify code for handling fewer than 200 bytes

The assembly code in crc32c-pcl-intel-asm_64.S is invoked only for
lengths >= 512, due to the overhead of saving and restoring FPU state.
Therefore, it is unnecessary for this code to be excessively "optimized"
for lengths < 200.  Eliminate the excessive unrolling of this part of
the code and use a more straightforward qword-at-a-time loop.

Note: the part of the code in question is not entirely redundant, as it
is still used to process any remainder mod 24, as well as any remaining
data when fewer than 200 bytes remain after least one 3072-byte chunk.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>