FRV: Specify the minimum slab/kmalloc alignment

Specify the minimum slab/kmalloc alignment to be 8 bytes.  This fixes a
crash when SLOB is selected as the memory allocator.  The FRV arch needs
this so that it can use the load- and store-double instructions without
faulting.  By default SLOB sets the minimum to be 4 bytes.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>