sh: wire up SET/GET_UNALIGN_CTL.

This hooks up the SET/GET_UNALIGN_CTL knobs cribbing the bulk of it from
the PPC and ia64 implementations. The thread flags happen to be the
logical inverse of what the global fault mode is set to, so this works
out pretty cleanly. By default the global fault mode is used, with tasks
now being able to override their own settings via prctl().

Signed-off-by: Paul Mundt <lethal@linux-sh.org>