efi/tpm: Differentiate missing and invalid final event log table.

Missing TPM final event log table is not a firmware bug.

Clearly if providing event log in the old format makes the final event
log invalid it should not be provided at least in that case.

Fixes: b4f1874c

 ("tpm: check event log version before reading final events")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>