smsc: smc911x: (HACK) force "active low" polarity for IRQ

IGEPv2 board needs to set the IRQ trigger polarity for the
SMSC911x LAN controller IRQ to active low.

The gpio-omap.txt documentation it says that #interrupt-cells
should be <2> and that a value of 8 is "active low level-sensitive".

But unfortunately, using this DT node definition:

&gpmc {
        ethernet@5,0 {
                pinctrl-names = "default";
                pinctrl-0 = <&smsc911x_pins>;
                compatible = "smsc,lan9221", "smsc,lan9115";
                reg = <5 0 0xff>; /* CS5 */
                interrupt-parent = <&gpio6>;
                interrupts = <16 8>; /* gpio line 176 */
                interrupt-names = "smsc911x irq";
                vmmc-supply = <&vddvario>;
                vmmc_aux-supply = <&vdd33a>;
                reg-io-width = <4>;

                smsc,save-mac-address;
      };
};

Does not work, since omap3.dtsi use an #interrupt-cells value of <1>
instead of <2>. This means that the second value for flags is omitted.

So, let's force the IRQ flags to IRQF_TRIGGER_LOW.

Also enable SMSC911x driver debug logs.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>