Fix build error in <linux/irq.h>

<linux/irq.h> relies on <linux/gfp.h> and <linux/topology.h> having been
included previous.  If not, the errors like below will result.

    CC      arch/mips/mti-malta/malta-int.o
  In file included from arch/mips/mti-malta/malta-int.c:25:
  include/linux/irq.h: In function ‘init_alloc_desc_masks’:
  include/linux/irq.h:444: error: implicit declaration of function ‘cpu_to_node’
  include/linux/irq.h:446: error: ‘GFP_ATOMIC’ undeclared (first use in this function)
  include/linux/irq.h:446: error: (Each undeclared identifier is reported only once
  include/linux/irq.h:446: error: for each function it appears in.)
  make[3]: *** [arch/mips/mti-malta/malta-int.o] Error 1
  make[2]: *** [arch/mips/mti-malta] Error 2
  make[1]: *** [sub-make] Error 2

Fixed by including the two missing headers.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>