mm: add 'is_special_page' inline function...

mm: add 'is_special_page' inline function...

... to cover xenheap and PGC_extra pages.

PGC_extra pages are intended to hold data structures that are associated
with a domain and may be mapped by that domain. They should not be treated
as 'normal' guest pages (i.e. RAM or page tables). Hence, in many cases
where code currently tests is_xen_heap_page() it should also check for
the PGC_extra bit in 'count_info'.

This patch therefore defines is_special_page() to cover both cases and
converts tests of is_xen_heap_page() (or open coded tests of PGC_xen_heap)
to is_special_page() where the page is assigned to a domain.

Signed-off-by: Paul Durrant <paul@xen.org>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <julien@xen.org>