[MIPS] *-berr: Header inclusions for DEC bus error handlers

 A fixup to add missing header inclusions for bus error handlers for
DECstation system after the recent switch to get_irq_regs().

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>