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

drivers/input/misc/pwm-beeper.c:147:12: warning: 'pwm_beeper_suspend' defined but not used [-Wunused-function]
drivers/input/misc/pwm-beeper.c:157:12: warning: 'pwm_beeper_resume' defined but not used [-Wunused-function]
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>