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.

This solution is not ideal 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.