In 4.x the semantics of MBEDTLS_PSA_CRYPTO_C and
MBEDTLS_PSA_CRYPTO_CLIENT are different compared with 3.6.
Where this is a problem, make guards more version-specific so that we
are guarding with MBEDTLS_PSA_CRYPTO_C for 3.6 and
MBEDTLS_PSA_CRYPTO_CLIENT for 4.x, keeping each branch the same as it
was formerly.
Signed-off-by: David Horstmann <david.horstmann@arm.com>