Update documentation by adding an example for DRA752 on DT description.

Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Rob Landley <rob@landley.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: J Keerthy <j-keerthy@ti.com>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>