cipher: bufhelp: allow unaligned memory accesses on ARM
* cipher/bufhelp.h [__arm__ && __ARM_FEATURE_UNALIGNED]: Enable BUFHELP_FAST_UNALIGNED_ACCESS.
Newer ARM systems support unaligned memory accesses and on gcc-4.7 and onwards
this is identified by __ARM_FEATURE_UNALIGNED macro.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>