lib/raid6: add ARM-NEON accelerated syndrome calculation

Rebased/reworked a patch contributed by Rob Herring that uses
NEON intrinsics to perform the RAID-6 syndrome calculations.
It uses the existing unroll.awk code to generate several
unrolled versions of which the best performing one is selected
at boot time.

Signed-off-by: Ard Biesheuvel <[email protected]>
Acked-by: Nicolas Pitre <[email protected]>
Cc: [email protected]
7 files changed