ARM: dts: omap4-droid4: Fix lost keypad slide interrupts for droid4

We may lose edge interrupts for gpio banks other than the first gpio
bank as they are not always powered. Instead, we must use the padconf
interrupt as that is always powered.

Note that we still also use the gpio for reading the pin state as that
can't be done with the padconf device.

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