x86: fix section mismatch warning in srat_64.c

Fix the following warnings:
WARNING: arch/x86/mm/built-in.o(.text+0x1abc): Section mismatch: reference to .init.data:nodes_parsed in 'unparse_node'
WARNING: arch/x86/mm/built-in.o(.text+0x1ac6): Section mismatch: reference to .cpuinit.data:apicid_to_node in 'unparse_node'
WARNING: arch/x86/mm/built-in.o(.text+0x1ad2): Section mismatch: reference to .cpuinit.data:apicid_to_node in 'unparse_node'

unparse_node are static and only used by acpi_scan_nodes which
is already annotated __init.
So we annotate unparse_node with __init.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>