asm/kregs.h isn't always included first, so we need an explicit include.

[Fix build breakage introduced by f21afc25
 smp.h: Use local_irq_{save,restore}() in !SMP version of on_each_cpu().]
Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>