ARM: dts: bcm281xx: use #include for device tree files

Replace /include/ by #include for bcm281xx device tree
files, enabling use of the C preprocessor.

Signed-off-by: Matt Porter <matt.porter@linaro.org>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Christian Daudt <csd@broadcom.com>