Tests: Add test for byte/short atomics on addresses which are not word-aligned

Add a unit test to catch architectures which do not allow byte and short
atomic operations on addresses which are not word aligned.

If an architecture supports byte and short atomic operations, it should
be valid to issue those operations on variables which are not
word-aligned, otherwise the architecture should not define
UATOMIC_HAS_ATOMIC_BYTE nor UATOMIC_HAS_ATOMIC_SHORT.

This should help identify architectures which mistakenly define
UATOMIC_HAS_ATOMIC_BYTE and UATOMIC_HAS_ATOMIC_SHORT.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I13d2f3be41749b018b39499106938b3746c419c1