arch/arm/Kconfig: enable unaligned capability for ARM

Change-Id: I7553c7a97e7fb0f07e0a95867df9b00583e10caf
Signed-off-by: faux123 <reioux@gmail.com>
ARM: use generic strnlen_user and strncpy_from_user functions

This patch implements the word-at-a-time interface for ARM using the
same algorithm as x86. We use the fls macro from ARMv5 onwards, where
we have a clz instruction available which saves us a mov instruction
when targetting Thumb-2. For older CPUs, we use the magic 0x0ff0001
constant. Big-endian configurations make use of the implementation from
asm-generic.

With this implemented, we can replace our byte-at-a-time strnlen_user
and strncpy_from_user functions with the optimised generic versions.

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
modified for Mako from LKML reference

Signed-off-by: Paul Reioux <reioux@gmail.com>

Conflicts:
	arch/arm/Kconfig

Change-Id: Id2e7b1fc54592c5b7c16239944cee614aa2393c0