omap-serial :Make the suspend/resume functions depend on CONFIG_PM_SLEEP.

    The macro SET_SYSTEM_SLEEP_PM_OPS  depends CONFIG_PM_SLEEP. The patch
    defines the suspend and resume functions for CONFIG_PM_SLEEP instead of
    CONFIG_SUSPEND.

Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>