xtensa: fix unaligned and load/store configuration interaction

Unaligned exception handler is needed in configurations with hardware
support for unaligned access when the load/store exception handler is
enabled because such configurations would still raise an exception on
unaligned access through the instruction bus.

Fixes: f29cf776

 ("xtensa: add load/store exception handler")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>