dt-bindings: display: Add ETM0700G0DH6 compatible string

The ETM0700G0DH6 is currently documented as using edt,etm070080dh6
compatible string, however the Linux kernel driver as well as a
couple of DTs use edt,etm0700g0dh6 compatible string. Add it into
the documentation.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Jan Tuerk <jan.tuerk@emtrion.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: devicetree@vger.kernel.org
To: dri-devel@lists.freedesktop.org
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190503154749.5630-1-marex@denx.de