openssl: fix crash on aarch64 if BTI is enabled but no Crypto instructions

On aarch64, if the processor doesn't have the Crypto instructions then
OpenSSL will fall back onto the "bit-sliced" assembler routines. When
branch protection (BTI) was enabled in OpenSSL these routines were
missed, so if BTI is available libssl will immediately abort when it
enters this assembler.

Backport a patch submitted upstream to add the required call target
annotations so that BTI doesn't believe the code is being exploited.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>