The type of PSA Diffie-Hellman group family identifiers. Values of this type are generally constructed by macros called `PSA_DH_FAMILY_xxx`. The group identifier is required to create a Diffie-Hellman key using the PSA_KEY_TYPE_DH_KEY_PAIR() or PSA_KEY_TYPE_DH_PUBLIC_KEY() macros. Values defined by this standard will never be in the range 0x80-0xff. Vendors who define additional families must use an encoding in this range.