[POWERPC] mpc8349emitx.dts: Setup USB-DR for peripheral mode.

Setup dr_mode for USB-DR to peripheral as the default (host mode) doesn't make
much sense for the mini-AB connector on the ITX board.

Peripheral mode is preferable to OTG as the fsl_usb2_udc.c driver doesn't yet
properly support it.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>