serial: omap: prevent runtime PM for "no_console_suspend"

The driver manages "no_console_suspend" by preventing runtime PM
during the suspend path, which forces the console UART to stay awake.

Reviewed-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>