serial: imx: add hibernation support

During hibernation, freeze/thaw/restore dev_pm_ops are called instead of
suspend/resume. Hook up the hibernation ops. The _noirq parts are
identical, but suspend/resume are replaced with variants that do not
enable wakeup from i.MX UART. There is no need to restore register
contents in thaw_noirq.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>