Make USE_PSA_INIT() and USE_PSA_DONE() available in all test suites in
all cases, doing nothing if MBEDTLS_USE_PSA_CRYPTO is disabled. Use
those in preference to having explicit
defined(MBEDTLS_USE_PSA_CRYPTO) checks (but there may still be places
left where using the new macros would be better).
Also provide PSA_INIT() by symmetry with PSA_DONE(), functional
whenver MBEDTLS_PSA_CRYPTO_C is enabled, but currently unused.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>