serial: omap: Add support for optional wake-up

With the recent pinctrl-single changes, omaps can treat
wake-up events from deeper idle states as interrupts.

There's a separate "io chain" controller on most omaps
that stays enabled when the device hits off-idle and the
regular interrupt controller is powered off.

Let's add support for the optional second interrupt for
wake-up events. And then serial-omap can manage the
wake-up interrupt from it's runtime PM calls to avoid
spurious interrupts during runtime.

Note that the wake interrupt is board specific as it
uses the UART RX pin, and for omap3, there are six pin
options for UART3 RX pin.

Also Note that the legacy platform based booting handles
the wake-ups in the legacy mux driver and does not need to
pass the wake-up interrupt to the driver.

And finally, to pass the wake-up interrupt in the dts file,
either interrupt-map or the pending interrupts-extended
property needs to be passed. It's probably best to use
interrupts-extended when it's available.

Cc: Felipe Balbi <balbi@ti.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>