dt/bindings: Remove references to linux,phandle properties

The linux,phandle property is essentially an internal structural element
of the DT data structure. The dtc toolchain takes care of maintaining it
at compile time. It does not need to appear as part of the binding
documentation. This patch removes it so that users don't think they need
to add a phandle property manually.

Signed-off-by: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>