x86_64: fix section mismatch warning in init.c

Fix following warning:
WARNING: vmlinux.o(.text+0x188ea): Section mismatch: reference to .init.text:__alloc_bootmem_core (between 'alloc_bootmem_high_node' and 'get_gate_vma')

alloc_bootmem_high_node() is only used from __init scope so declare it __init.
And in addition declare the weak variant __init too.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/sparse.c

@@ -209,7 +209,7 @@ static int __meminit sparse_init_one_section(struct mem_section *ms,
 	return 1;
 }
 
-__attribute__((weak))
+__attribute__((weak)) __init
 void *alloc_bootmem_high_node(pg_data_t *pgdat, unsigned long size)
 {
 	return NULL;