s390x: Return specification exception for unimplemented diag 308 subcodes

s390x: Return specification exception for unimplemented diag 308 subcodes

The architecture specifies specification exceptions for all
unavailable subcodes.

The presence of subcodes is indicated by checking some query subcode.
For example 6 will indicate that 3-6 are available. So future systems
might call new subcodes to check for new features. This should not
trigger a hw error, instead we return the architectured specification
exception.

Signed-off-by: Janosch Frank <[email protected]>
Cc: [email protected]
Message-Id: <20190111113657[email protected]>
Reviewed-by: Christian Borntraeger <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>