tfm: Add mbedtls_ecc_group_to_psa.h to crypto_extra.h

Include mbedtls_ecc_group_to_psa.h from crypto_extra.h so that clients
of PSA within Mbed OS do not need to behave differently depending on
which PSA implementation they are using.

XXX I don't much like this solution as it makes it more difficult to
update the TF-M-provided psa/crypto_extra.h. We'll have to see what
other options we have for including additional headers based on the Mbed
OS configuration.

Author: Patater

platform/FEATURE_EXPERIMENTAL_API/FEATURE_PSA/TARGET_TFM/TARGET_TFM_LATEST/include/psa/crypto_extra.h

@@ -57,6 +57,8 @@ extern "C" {
 
 /**@}*/
 
+#include "mbedtls_ecc_group_to_psa.h"
+
 #ifdef __cplusplus
 }
 #endif