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>
 {
        if (omap2_fclks_active())
                return 0;
+       if (!omap_uart_can_sleep())
+               return 0;
        if (osc_ck->usecount > 1)
                return 0;
        if (omap_dma_running())