ARM: dts: TWL4030: fix mux and wakeup for SYS_NIRQ line

On most OMAP3 platforms, the twl4030 IRQ line is connected to the
SYS_NIRQ line on OMAP.  Add another DTS include file
(twl4030_omap3.dtsi) for boards that hook up the twl4030 this way
to include.

This allows RTC wake from off-mode to work again on OMAP3-based
platforms with twl4030.  Tested on 3530/Beagle, 3730/Beagle-xM,
3530/Overo, 3730/Overo-STORM.

Special thanks to Florian Vaussard for suggesting use of preprocessor
feature.

Cc: Florian Vaussard <florian.vaussard@epfl.ch>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>