BCM270X_DT: Don't generate "linux,phandle" props

The EPAPR standard says to use "phandle" properties to store phandles,
rather than the deprecated "linux,phandle" version. By default, dtc
generates both, but adding "-H epapr" causes it to only generate
"phandle"s, saving some space and clutter.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>