pk/psa: use PSA guard for mbedtls_ecc_group_to_psa() and mbedtls_ecc_group_of_psa()

This allows also to:
- removing the dependency on ECP_C for these functions and only rely
  on PSA symbols
- removing extra header inclusing from crypto_extra.h
- return MBEDTLS_PK_USE_PSA_EC_DATA and MBEDTLS_PK_HAVE_ECC_KEYS to
  their original position in pk.h

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index d6723b2..2173483 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -390,7 +390,7 @@
 /* Key management */
 /****************************************************************/
 
-#if defined(MBEDTLS_PK_HAVE_ECC_KEYS)
+#if defined(PSA_WANT_KEY_TYPE_ECC_PUBLIC_KEY)
 psa_ecc_family_t mbedtls_ecc_group_to_psa(mbedtls_ecp_group_id grpid,
                                           size_t *bits)
 {
@@ -531,7 +531,7 @@
     (void) bits_is_sloppy;
     return MBEDTLS_ECP_DP_NONE;
 }
-#endif /* MBEDTLS_PK_HAVE_ECC_KEYS */
+#endif /* PSA_WANT_KEY_TYPE_ECC_PUBLIC_KEY */
 
 psa_status_t psa_validate_unstructured_key_bit_size(psa_key_type_t type,
                                                     size_t bits)