cryptsetup-tokens: Print tpm2-primary-alg: only when it is known

cryptsetup-tokens: Print tpm2-primary-alg: only when it is known

When 'tpm2-primary-alg' is missing in LUKS JSON token, the output of
'cryptsetup luksDump' is always:

	tpm2-primary-alg: ecc

because tpm2_parse_luks2_json() returns the default (TPM2_ALG_ECC). This can be
misleading and wrong. Make tpm2_parse_luks2_json() return the reality and move
the default to tpm2_unseal().

(cherry picked from commit 4883ef8aae80b0c1e69047c83b3830b9675db8e3)
(cherry picked from commit 0b4f049ecc8c69ef8b0671e762e9cbe3cd6284ab)
(cherry picked from commit b69a842e11fd70f9b6a31d6d42e09b5d434c114c)