i.MX31: Add support for the CPLD on PDK Debug board.

The i.MX31 PDK consists of several boards, one of them is a debug
board containing a CPLD which controls some debug leds, switch
buttons, an interrupt chip and an Ethernet controller.
This patch adds support for detecting if the PDK board is present
(during boot) and adds the interrupt chip to the kernel.

Signed-off-by: Magnus Lilja <lilja.magnus@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>