x86: move max_pfn_mapped and max_low_pfn_mapped to setup.c

This patch moves the max_pfn_mapped and max_low_pfn_mapped global
variables to kernel/setup.c where they're initialized.

[ Impact: cleanup ]

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
LKML-Reference: <1240923649.1982.21.camel@penberg-laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>