mmc: sdhci-spear: add CONFIG_PM_SLEEP to suspend/resume functions

Add CONFIG_PM_SLEEP to suspend/resume functions to fix the following
build warning when CONFIG_PM_SLEEP is not selected. This is because
sleep PM callbacks defined by SIMPLE_DEV_PM_OPS are only used when
the CONFIG_PM_SLEEP is enabled.

drivers/mmc/host/sdhci-spear.c:295:12: warning: 'sdhci_suspend' defined but not used [-Wunused-function]
drivers/mmc/host/sdhci-spear.c:308:12: warning: 'sdhci_resume' defined but not used [-Wunused-function]

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>