p2m: split mem_access into separate files

This patch relocates mem_access components that are currently mixed with p2m
code into separate files. This better aligns the code with similar subsystems,
such as mem_sharing and mem_paging, which are already in separate files. There
are no code-changes introduced, the patch is mechanical code movement.

On ARM we also relocate the static inline gfn_next_boundary function to p2m.h
as it is a function the mem_access code needs access to.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

MAINTAINERS

@@ -402,6 +402,8 @@ S:	Supported
 F:	tools/tests/xen-access
 F:	xen/arch/*/monitor.c
 F:	xen/arch/*/vm_event.c
+F:	xen/arch/arm/mem_access.c
+F:	xen/arch/x86/mm/mem_access.c
 F:	xen/arch/x86/hvm/monitor.c
 F:	xen/common/mem_access.c
 F:	xen/common/monitor.c