ARM: dts: imx6: edmqmx6: Add PCIe support

Add support for the PCI express bus available on MX6 Data Modul
edm-qmx6 board.

Signed-off-by: Silvio Fricke <silvio.fricke@gmail.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>