CONFIG_PM will be set if either or both CONFIG_PM_SLEEP and
CONFIG_PM_RUNTIME is set. Compiling the driver with !CONFIG_PM_SLEEP causes
following compilation warning:

drivers/spi/spi-pxa2xx.c:1270:12: warning: ‘pxa2xx_spi_suspend’ defined but not used [-Wunused-function]

Fix this by using CONFIG_PM_SLEEP instead.
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: NMark Brown <broonie@linaro.org>