ARM: dts: add RealView EB rev D A9 MPCore variant

The Cortex A9 MPCore tile can be mounted on top of the revision
D variant of the RealView EB, so create another variant of the
DTS file for this.

arm-realview-eb-a9mp = mounted on pre-revision D baseboard
arm-realview-eb-a9mp-bbrevd = mounted on the revision D baseboard

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>