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/include/psa/crypto_extra.h b/include/psa/crypto_extra.h
index cfa7a67..5529dd1 100644
--- a/include/psa/crypto_extra.h
+++ b/include/psa/crypto_extra.h
@@ -572,8 +572,7 @@
 /** \defgroup psa_tls_helpers TLS helper functions
  * @{
  */
-#include <mbedtls/pk.h>
-#if defined(MBEDTLS_PK_HAVE_ECC_KEYS)
+#if defined(PSA_WANT_KEY_TYPE_ECC_PUBLIC_KEY)
 #include <mbedtls/ecp.h>
 
 /** Convert an ECC curve identifier from the Mbed TLS encoding to PSA.
@@ -614,7 +613,7 @@
 mbedtls_ecp_group_id mbedtls_ecc_group_of_psa(psa_ecc_family_t curve,
                                               size_t bits,
                                               int bits_is_sloppy);
-#endif /* MBEDTLS_PK_HAVE_ECC_KEYS */
+#endif /* PSA_WANT_KEY_TYPE_ECC_PUBLIC_KEY */
 
 /**@}*/