sh: Add sh7724 notifier for R-standby save/restore

Make use of the recently added notifier chains for sh7724
r-standby register save/restore handling. At this point
only the BSC and INTC are handled.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>