[ARM] 4946/1: pxa3xx: Print an error if we refuse to suspend

The PXA3xx will not suspend if there are no wakeup sources configured.
Print a diagnostic message to make it easier for the user to see what's
happening.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: eric miao <eric.y.miao@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>