test: align ec_pub public keyfile with its ec_prv.sec1 counterpart

This change affects:
- both PEM and DER files, since they contain the same public key
  only in different formats
- "ec_pub.comp.pem" since it's the same as "ec_pub.pem" but in
  compressed format

The makefile was also updated accordingly to reflect these
dependencies.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 47370b4..c008030 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -935,6 +935,9 @@
 	$(OPENSSL) pkey -in $< -inform DER -out $@
 all_final += ec_prv.pk8param.pem
 
+ec_pub.der: ec_prv.sec1.der
+	$(OPENSSL) pkey -in $< -inform DER -outform DER -pubout -out $@
+
 ec_prv.sec1.comp.pem: ec_prv.sec1.pem
 	$(OPENSSL) ec -in $< -out $@ -conv_form compressed
 all_final += ec_prv.sec1.comp.pem