[libata] scsi: support MODE SENSE request for changeable and default parameters

Since the next patch will introduce support for MODE SELECT, it
makes sense to start advertising which bits are actually changeable.
For now, the answer is none.

Default parameters can also be reported, they are simply the same
as the current parameters.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>