ARM: dts: OMAP4: Fix ethernet IRQ for OMAP4 boards

Commit ff5c9059 (ARM: dts: OMAP3+: Correct gpio #interrupts-cells
property) updated the number of interrupt cells required for configuring
gpios as interrupts for other devices (such as ethernet controllers).
This update allowed the interrupt type (edge, level, etc) to be
configured via device-tree (as described in the
Documentation/devicetree/bindings/gpio/gpio-omap.txt).

This broke ethernet support on the OMAP4 SDP board that defines a gpio
as the ethernet IRQ because the interrupt type (level, edge, etc) was
not getting configured correctly. This board use the ks8851 ethernet
chip which has an active low interrupt. Fix this by defining the gpio
interrupt as active-low in the device-tree binding.

Please note that the OMAP4-VAR-SOM also uses the same ethernet
controller and it is expected it will have the same problem. So the
same fix is also applied to this board.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>