hw/scsi: Concentrate -drive if=scsi auto-create in one place

hw/scsi: Concentrate -drive if=scsi auto-create in one place

The logic to create frontends for -drive if=scsi is in SCSI HBAs.  For
all other interface types, it's in machine initialization code.

A few machine types create the SCSI HBAs necessary for that.  That's
also not done for other interface types.

I'm going to deprecate these SCSI eccentricities.  In preparation for
that, create the frontends in main() instead of the SCSI HBAs, by
calling new function scsi_legacy_handle_cmdline() there.

Note that not all SCSI HBAs create frontends.  Take care not to change
that.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1487161136-9018-2-git-send-email-armbru@redhat.com>
Acked-By: Paolo Bonzini <pbonzini@redhat.com>