Instead of using the legacy mbedtls_ecp_check_pub_priv() function which
was based on ECP math, we add a new option named eckey_check_pair_psa()
which takes advantage of PSA.
Of course, this is available when MBEDTLS_USE_PSA_CRYPTO in enabled.
Tests were also fixed accordingly.
Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>