Make cpu_suspend()..return function preserve r4 to r11 across a suspend
cycle.  This is in preparation of relieving platform support code from
this task.
Acked-by: NFrank Hofmann <frank.hofmann@tomtom.com>
Tested-by: NKevin Hilman <khilman@ti.com>
Acked-by: NJean Pihet <j-pihet@ti.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>