Features
   * Some crypto modules that previously depended on MD or a low-level hash
     module, either unconditionally (RSA, PK, PKCS5, PKCS12, EC J-PAKE), or
     for some features (PEM for encrypted files), are now able to use PSA
     Crypto instead when the legacy API is not available. This means it is
     now possible to use all features from those modules in configurations
     where the built-in implementations of hashes are excluded and the hashes
     are only provided by PSA drivers. In these configurations, you need to
     call `psa_crypto_init()` before you call any function from those
     modules; this is not required in configurations where the built-in
     implementation is still available. Note that for modules that use MD
     (RSA, PKCS5, PKCS12, EC J-PAKE) in builds that have MBEDTLS_MD_C enabled,
     all hashes used with those modules need to be built-in, as drivers are only
     used when MBEDTLS_MD_C is disabled; configurations where some hashes are
     available as built-ins, and some only from drivers, are currently not
     supported. Also note that some crypto modules and features still depend on
     the built-in implementation of hashes: MBEDTLS_HKDF_C (but the PSA HKDF
     functions do not depend on it), MBEDTLS_ENTROPY_C, MBEDTLS_HMAC_DRBG_C and
     MBEDTLS_ECDSA_DETERMINISTIC. In particular, for now, compiling without
     built-in hashes requires use of MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG.
   * When MBEDTLS_USE_PSA_CRYPTO is enabled, X.509, TLS 1.2 and TLS 1.3 no
     longer depend on MD. This means it is now possible to use them in
     configurations where the built-in implementations of hashes are excluded
     and the hashes are only provided by PSA drivers.

Features
   * Some modules can now use PSA drivers for hashes, including with no
     built-in implementation present, but only in some configurations.
     - RSA PKCS#1 v2.1, PKCS5, PKCS12 and EC J-PAKE now use hashes from PSA
       when (and only when) MBEDTLS_MD_C is disabled.
     - PEM parsing of encrypted files now uses MD-5 from PSA when (and only
       when) MBEDTLS_MD5_C is disabled.
     See the documentation of the corresponding macros in mbedtls_config.h for
     details.
     Note that some modules are not able to use hashes from PSA yet, including
     the entropy module. As a consequence, for now the only way to build with
     all hashes only provided by drivers (no built-in hash) is to use
     MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG.
   * When MBEDTLS_USE_PSA_CRYPTO is enabled, X.509, TLS 1.2 and TLS 1.3 now
     properly negotiate/accept hashes based on their availability in PSA.
     As a consequence, they now work in configurations where the built-in
     implementations of (some) hashes are excluded and those hashes are only
     provided by PSA drivers. (See previous entry for limitation on RSA-PSS
     though: that module only use hashes from PSA when MBEDTLS_MD_C is off).

Improve ChangeLog entry for driver-only hashes
Improve ChangeLog entry for driver-only hashes

- avoid long unstructured paragraph with long messy sentences
- de-emphasize "no longer depends on MD" and emphasize "can work in
some driver-only builds" instead - that's what users are interested in
(building without MD is just the current way to accomplish that, but
that will change in the future)

Signed-off-by: Manuel Pégourié-Gonnard <4ba0d615aeeda88e422ca8fba28fe2938485facf@arm.com>
