board: ten64: strip extra u-boot compatibles from FDT

The u-boot version of the LS1088A device tree has
an extra compatible (simple-mfd) added to &fsl_mc
to facilitate usage with U-Boot's device model.

Unfortunately FreeBSD will only match the single
"fsl,qoriq-mc" exactly when the node is a "bus"
object, so we need to strip out the extra compatible
before presenting it to the operating system.

Signed-off-by: Mathew McBride <matt@traverse.com.au>
Reviewed-by: Peng Fan <peng.fan@nxp.com>