ARM: OMAP4: PM: Avoid expensive cpu_suspend() path for all CPU power states except off

Current CPU PM code code make use of common cpu_suspend() path for all the
CPU power states which is not optimal. In fact cpu_suspend() path is needed
only when we put CPU power domain to off state where the CPU context is lost.

Update the code accordingly so that the expensive cpu_suspend() path
can be avoided for the shallow CPU power states like CPU PD INA/CSWR.

The patch has been tested on OMAP4430 and OMAP5430(with few out of tree patches)
devices for suspend and CPUidle.

Cc: Kevin Hilman <khilman@deeprootsystems.com>
Reported-by: NRichard Woodruff <r-woodruff2@ti.com>
Signed-off-by: NSantosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: NKevin Hilman <khilman@linaro.org>

arch/arm/mach-omap2/omap-mpuss-lowpower.c

@@ -246,7 +246,10 @@ int omap4_enter_lowpower(unsigned int cpu, unsigned int power_state)
 	/*
 	 * Call low level function  with targeted low power state.
 	 */
-	cpu_suspend(save_state, omap4_finish_suspend);
+	if (save_state)
+		cpu_suspend(save_state, omap4_finish_suspend);
+	else
+		omap4_finish_suspend(save_state);
 
 	/*
 	 * Restore the CPUx power state to ON otherwise CPUx