x86_64: fix section mismatch warnings in tce

Fix the following two section mismatch warnings:

WARNING: vmlinux.o(.text+0x1ce84): Section mismatch: reference to .init.text:free_bootmem (between 'free_tce_table' and 'build_tce_table')
WARNING: vmlinux.o(.text+0x1d04d): Section mismatch: reference to .init.text:__alloc_bootmem_low (between 'alloc_tce_table' and 'kretprobe_trampoline_holder')

In both cases the functions was used only from __init
context so mark them __init.

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