gnttab: delay allocation of sub structures

gnttab: delay allocation of sub structures

Delay the allocation of the grant table sub structures in order to
allow modifying parameters needed for sizing of these structures at a
per domain basis. Allocate the structures and the table frames only
from grant_table_init().

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>