pk: align library and tests code to the new internal functions

Note = programs are not aligned to this change because:
- the original mbedtls_pk_ec is not ufficially deprecated
- that function is used in tests when ECP_C is defined, so
  the legacy version of that function is available in that
  case

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/suites/test_suite_pkparse.function b/tests/suites/test_suite_pkparse.function
index 838a7db..e0e3300 100644
--- a/tests/suites/test_suite_pkparse.function
+++ b/tests/suites/test_suite_pkparse.function
@@ -3,6 +3,7 @@
 #include "mbedtls/pem.h"
 #include "mbedtls/oid.h"
 #include "mbedtls/ecp.h"
+#include "pk_internal.h"
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -83,9 +84,9 @@
     TEST_ASSERT(res == result);
 
     if (res == 0) {
-        mbedtls_ecp_keypair *eckey;
+        const mbedtls_ecp_keypair *eckey;
         TEST_ASSERT(mbedtls_pk_can_do(&ctx, MBEDTLS_PK_ECKEY));
-        eckey = mbedtls_pk_ec(ctx);
+        eckey = mbedtls_pk_ec_ro(ctx);
         TEST_ASSERT(mbedtls_ecp_check_pubkey(&eckey->grp, &eckey->Q) == 0);
     }
 
@@ -110,9 +111,9 @@
     TEST_ASSERT(res == result);
 
     if (res == 0) {
-        mbedtls_ecp_keypair *eckey;
+        const mbedtls_ecp_keypair *eckey;
         TEST_ASSERT(mbedtls_pk_can_do(&ctx, MBEDTLS_PK_ECKEY));
-        eckey = mbedtls_pk_ec(ctx);
+        eckey = mbedtls_pk_ec_ro(ctx);
         TEST_ASSERT(mbedtls_ecp_check_privkey(&eckey->grp, &eckey->d) == 0);
     }