x86: fix kernel_physical_mapping_init() for large x86 systems

x86: fix kernel_physical_mapping_init() for large x86 systems

based on e22146e610bb7aed63282148740ab1d1b91e1d90 upstream

Fix bug in kernel_physical_mapping_init() that causes kernel
page table to be built incorrectly for systems with greater
than 512GB of memory.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Cc: linux-mm@kvack.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Oliver Pinter <oliver.pntr@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>