x86: move saving e820_saved to setup_memory_map

so other path that will override memory_setup or
machine_specific_memory_setup could have e820_saved too.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>