x86: silence section mismatch warning - get_local_pda

Take out part of get_local_pda referencing __init function (free_bootmem)
to new (static) function marked as __ref. It's safe to do because free_bootmem
is called before __init sections are dropped.

WARNING: vmlinux.o(.cpuinit.text+0x3cd7): Section mismatch in reference from the function get_local_pda() to the function .init.text:free_bootmem()
The function __cpuinit get_local_pda() references
a function __init free_bootmem().
If free_bootmem is only used by get_local_pda then
annotate free_bootmem with a matching annotation.

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>