target/hexagon: raise SIGBUS on unaligned scalar stores

hexagon-linux-user had no enforcement of alignment for scalar store
exceptions, and unaligned stores silently succeeded instead of raising
SIGBUS.

Stores are logged rather than committed immediately, so both commit
paths need the fix.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Reviewed-by: Matheus Tavares Bernardino <matheus.bernardino@oss.qualcomm.com>
Signed-off-by: Brian Cain <brian.cain@oss.qualcomm.com>