vdsmapi-schema: optional/required params fix

- VideoDevice specParams field 'vram' is required according to
current dom getXML
- Smartcard device was previously missing required parameters
mode and type
- Type is actually required only for passthrough mode, fixed in code and
  definition

Change-Id: Ia4f9e123da73b0a326ce0762702e5ab7a3a0a583
Signed-off-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/18056
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Michal Skrivanek <michal.skrivanek@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>