cryptenroll: Save primary algorithm type to the LUKS token

cryptenroll: Save primary algorithm type to the LUKS token

'tpm2-primary-alg' field is currently unset in LUKS JSON token both for the
case when SRK was used for enrolling (--tpm2-device-key=) and for the case when
SRK was obtained/generated (--tpm2-device=). While this information is not
really needed for unsealing (the sealed object itself has key type in it), it
may be convenient to see key type in e.g. 'cryptsetup luksDump' in the
situations where key type matters. Since 'tpm2-primary-alg' is already defined,
just set it properly in all cases.