crypto: n2 - make of_device_ids const

of_device_ids are not supposed to change at runtime. All functions
working with of_device_ids provided by <linux/of.h> work with const
of_device_ids. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   2001	   2168	     48	   4217	   1079	drivers/crypto/n2_core.o

File size after constify dummy_tlb_ops.:
   text	   data	    bss	    dec	    hex	filename
   3601	    536	     48	   4185	   1059	drivers/crypto/n2_core.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>