common: add a new mappable resource type: XENMEM_resource_grant_table

common: add a new mappable resource type: XENMEM_resource_grant_table

This patch allows grant table frames to be mapped using the
XENMEM_acquire_resource memory op.

NOTE: This patch expands the on-stack mfn_list array in acquire_resource()
      but it is still small enough to remain on-stack.

NOTE: This patch also removes a bogus comment above the
      grant_to_status_frames() function.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
[Rebase over "Explicitly default to gnttab v1 during domain creation"]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>