x86: move save_mr() into .meminit.text

Impact: cleanup, save memory

The function is only being called from boot or memory hotplug paths.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <49B910B6.76E4.0078.0@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>