crypto: x86/curve25519 - disable gcov

curve25519-x86_64.c fails to build when CONFIG_GCOV_KERNEL is enabled.
The error is "inline assembly requires more registers than available"
thrown from the `fsqr()` function. Therefore, excluding this file from
GCOV profiling until this issue is resolved. Thereby allowing
CONFIG_GCOV_PROFILE_ALL to be enabled for x86.
Signed-off-by: Joe Fradley <joefradley@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/x86/crypto/Makefile

@@ -107,3 +107,6 @@ quiet_cmd_perlasm = PERLASM $@
       cmd_perlasm = $(PERL) $< > $@
 $(obj)/%.S: $(src)/%.pl FORCE
 	$(call if_changed,perlasm)
+
+# Disable GCOV in odd or sensitive code
+GCOV_PROFILE_curve25519-x86_64.o := n