tools/dombuilder: Prevent failures of xc_dom_gnttab_init()

tools/dombuilder: Prevent failures of xc_dom_gnttab_init()

Recent changes in grant table configuration have caused calls to
xc_dom_gnttab_init() to fail if not proceeded with a call to
xc_domain_set_gnttab_limits().  This is backwards from the point of view of
3rd party dombuilder users.

Add max_{grant,maptrack}_frames parameters to struct xc_dom_image, and require
them to be set by callers using xc_dom_gnttab_init().  Libxl, which uses
xc_dom_gnttab_init() itself is updated appropriately.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Tested-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>