Add parity generation/rebuild using AVX-512 for x86-64

avx512f should work on all AVX512 hardware, since it only uses
Foundation instructions.

avx512bw should be faster on hardware supporting the AVW512BW
extension. We can use full-width pshufb (instead of relying on the 256
bits AVX2 pshufb). As a side-effect, the code is also unrolled more.

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Gvozden Neskovic <neskovic@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Romain Dolbeau <romain.github@dolbeau.name>
Closes #5219

cmd/raidz_test/raidz_test.h

@@ -34,6 +34,8 @@ static const char *raidz_impl_names[] = {
 	"sse2",
 	"ssse3",
 	"avx2",
+	"avx512f",
+	"avx512bw",
 	"aarch64_neon",
 	"aarch64_neonx2",
 	NULL