OMAP2: PM: check UART status before trying to idle

As is done on OMAP3, check omap_uart_can_sleep() as one of the
pre-conditions for entering the idle loop.  Without this check,
entering idle introduces large latencies on active UARTs, and is
especially noticable on serial console.
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/pm24xx.c

@@ -245,6 +245,8 @@ static int omap2_can_sleep(void)
 {
 	if (omap2_fclks_active())
 		return 0;
+	if (!omap_uart_can_sleep())
+		return 0;
 	if (osc_ck->usecount > 1)
 		return 0;
 	if (omap_dma_running())