m68knommu: fix build error due to the lack of find_next_bit_le()

m68knommu can't build ext4, udf, and ocfs2 due to the lack of
find_next_bit_le().

This implements find_next_bit_le() on m68knommu by duplicating the generic
find_next_bit_le() in lib/find_next_bit.c.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>