Add Wisun Fan device certificate

Add certificate with Wisun fan device extended key usage,
support parsing it and add tests.
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index d139bfa..d1af18c 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -184,6 +184,9 @@
 server5-unsupported_othername.crt: server5.key
 	$(OPENSSL) req -x509 -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS unsupported othername SAN" -set_serial 77 -config $(test_ca_config_file) -extensions unsupoported_othername_san -days 3650 -sha256 -key $< -out $@
 
+server5-fan.crt: server5.key
+	$(OPENSSL) req -x509 -new -subj "/C=UK/O=Mbed TLS/CN=Mbed TLS FAN" -set_serial 77 -config $(test_ca_config_file) -extensions fan_cert -days 3650 -sha256 -key server5.key -out $@
+
 server10-badsign.crt: server10.crt
 	{ head -n-2 $<; tail -n-2 $< | sed -e '1s/0\(=*\)$$/_\1/' -e '1s/[^_=]\(=*\)$$/0\1/' -e '1s/_/1/'; } > $@
 all_final += server10-badsign.crt