MAINTAINERS: Add file patterns for qcom device tree bindings

Submitters of device tree binding documentation may forget to CC
the subsystem maintainer if this is missing.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andy Gross <andy.gross@linaro.org>
Cc: David Brown <david.brown@linaro.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: linux-soc@vger.kernel.org
Signed-off-by: Andy Gross <andy.gross@linaro.org>