bitops: introduce CONFIG_GENERIC_FIND_BIT_LE

This introduces CONFIG_GENERIC_FIND_BIT_LE to tell whether to use generic
implementation of find_*_bit_le() in lib/find_next_bit.c or not.

For now we select CONFIG_GENERIC_FIND_BIT_LE for all architectures which
enable CONFIG_GENERIC_FIND_NEXT_BIT.

But m68knommu wants to define own faster find_next_zero_bit_le() and
continues using generic find_next_{,zero_}bit().
(CONFIG_GENERIC_FIND_NEXT_BIT and !CONFIG_GENERIC_FIND_BIT_LE)

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