x86: mm/discontig_32.c: make code static

node0_bdata and paddr_to_nid() can become static.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>