x86/mm: Mark arch_ioremap_p{m,u}d_supported() __init

... as their only caller is.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
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/5566EE07020000780007E683@mail.emea.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>