Implement char/short_load primitives for ARMv6+

Implement char/short_load primitives for ARMv6+

* src/atomic_ops/sysdeps/armcc/arm_v6.h: Include all_atomic_only_load.h
(with defined AO_ACCESS_CHECK_ALIGNED, AO_ACCESS_short_CHECK_ALIGNED
and AO_ACCESS_int_CHECK_ALIGNED).
* src/atomic_ops/sysdeps/gcc/arm.h: Likewise.
* src/atomic_ops/sysdeps/armcc/arm_v6.h (AO_load, AO_HAVE_load):
Remove (since defined by all_atomic_only_load.h).
* src/atomic_ops/sysdeps/gcc/arm.h (AO_load, AO_HAVE_load): Likewise.
* src/atomic_ops/sysdeps/gcc/arm.h: Adjust atomic_store.h filename in
comment.