pk: move ECC setters to a separate file

- These functions are used both in pkparse.c for key parsing
  as well as pk.c for managing copy_from_psa(). As as consequence
  they should belong to pk.c, but that would make that module
  messier, so that's why a new separate module is added.
- Their guard can be changed from PKPARSE_C to PK_C.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/Makefile b/library/Makefile
index d11a98d..bef4335 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -125,6 +125,7 @@
 	     padlock.o \
 	     pem.o \
 	     pk.o \
+	     pk_ecc.o \
 	     pk_wrap.o \
 	     pkcs12.o \
 	     pkcs5.o \