x86/boot: Make the x86_init noop functions static

Make the noop functions in x86_init.c static in case they are used
locally only.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180221094232.23462-1-jgross@suse.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>