serial: 8250_omap: Drop pm_runtime_irq_safe()

Let's drop the use of pm_runtime_irq_safe() for 8250_omap. The use of
pm_runtime_irq_safe() is not nice as it takes a permanent usage count on
the parent device.

We can finally drop pm_runtime_irq_safe() safely as the kernel now knows
when the uart port tx is active. This changed with commit 84a9582fd203
("serial: core: Start managing serial controllers to enable runtime PM").

For serial port rx, we already use Linux generic wakeirqs for 8250_omap.

To drop pm_runtime_irq_safe(), we need to add handling for shallow idle
state where the port hardware may already be awake and an IO interrupt
happens. We also need to replace the serial8250_rpm sync calls in the
interrupt handlers with async runtime PM calls.

Note that omap8250_irq() calls omap_8250_dma_handle_irq(), so we don't
need separate runtime PM calls in omap_8250_dma_handle_irq().

While at it, let's also add the missing line break to the end of
omap8250_runtime_resume() to group the calls.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20231004062650.64487-1-tony@atomide.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>