sha/asm/sha512p8-ppc.pl: add POWER8 performance data.
[skip ci]
# for sha1-ppc.pl - 73%. 100% means that multi-process result equals
# to single-process one, given that all threads end up on the same
# physical core.
+#
+######################################################################
+# Believed-to-be-accurate results in cycles per processed byte [on
+# little-endian system]. Numbers in square brackets are for 64-bit
+# build of sha512-ppc.pl, presented for reference.
+#
+# POWER8
+# SHA256 9.9 [15.8]
+# SHA512 6.3 [10.3]
$flavour=shift;
$output =shift;
