Also detect Armv8.2 SHA-512 extensions on FreeBSD.

A small follow-up to
https://boringssl-review.googlesource.com/c/boringssl/+/54105, to bring
it up to feature parity with the other aarch64 backends.
ID_AA64ISAR0_SHA2_512 seems to be present in FreeBSD 12.0, so I don't
believe this needs any compatibility ifdefs.

Bug: 505
Change-Id: I44891cf635adfd2ae26d4113fdc910549cf89193
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/54725
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Reviewed-by: Robert Clausecker <fuzxxl@gmail.com>
Reviewed-by: Bob Beck <bbe@google.com>

crypto/cpu_aarch64_freebsd.c

diff --git a/crypto/cpu_aarch64_freebsd.c b/crypto/cpu_aarch64_freebsd.c
index 462a0be..42d8afa 100644
--- a/crypto/cpu_aarch64_freebsd.c
+++ b/crypto/cpu_aarch64_freebsd.c
@@ -54,6 +54,9 @@
   if (ID_AA64ISAR0_SHA2_VAL(id_aa64isar0) >= ID_AA64ISAR0_SHA2_BASE) {
     OPENSSL_armcap_P |= ARMV8_SHA256;
   }
+  if (ID_AA64ISAR0_SHA2_VAL(id_aa64isar0) >= ID_AA64ISAR0_SHA2_512) {
+    OPENSSL_armcap_P |= ARMV8_SHA512;
+  }
 }
 
 #endif  // OPENSSL_AARCH64 && OPENSSL_FREEBSD && !OPENSSL_STATIC_ARMCAP