boards: nxp: Change default mac to unique for some

Change the default of the mac address for a few example boards
to use the "unique" option based on the chip unique ID,
instead of random. The RW was chosen because it has HWINFO implemented
currently. RT1050 was chosen as one of the RT boards.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>