ChangeLog: add note for removal of DHM related functions in SSL

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>

ChangeLog.d/9956.txt

+Removals
+   * Following the removal of DHM module (#9972 and TF-PSA-Crypto#175) the
+     following SSL functions are removed:
+     - mbedtls_ssl_conf_dh_param_bin
+     - mbedtls_ssl_conf_dh_param_ctx
+     - mbedtls_ssl_conf_dhm_min_bitlen