ARM: dts: omap: Remove WAKEUPENABLE mux options for UARTs

This is no longer needed as the device specific wake-up event
can now be specified with interrupts-extended property where
the second interrupt is the pinctrl-single register, such as
the UART3 RX pin.

Note that twl4030_omap3.dtsi needs to set WAKEUPENABLE for
off-idle to properly trigger the PMIC scripts. And GPIO pins
still need to set WAKEUPENABLE for wake-up events.

Signed-off-by: Tony Lindgren <tony@atomide.com>