PSA_TLS12_PSK_TO_MS_PSK_MAX_SIZE macro

This macro returns the maximum supported length of the PSK for the TLS-1.2 PSK-to-MS key derivation (#PSA_ALG_TLS12_PSK_TO_MS(\c hash_alg)). The maximum supported length does not depend on the chosen hash algorithm. Quoting RFC 4279, Sect 5.3: TLS implementations supporting these ciphersuites MUST support arbitrary PSK identities up to 128 octets in length, and arbitrary PSKs up to 64 octets in length. Supporting longer identities and keys is RECOMMENDED. Therefore, no implementation should define a value smaller than 64 for #PSA_TLS12_PSK_TO_MS_PSK_MAX_SIZE.