Updates to documentation (#280)

Documentation updates (including moving of header files

lib_xua/doc/rst/opt_pdm.rst

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+
+PDM Microphones
+~~~~~~~~~~~~~~~
+
+The codebase supports input from up to 8 PDM microphones. 
+
+PDM microphone support is provided via ``lib_mic_array``.  Settings for PDM microphones are controlled
+via the defines in :ref:`opt_pdm_defines`. 
+
+.. _opt_pdm_defines:
+
+.. list-table:: PDM defines
+   :header-rows: 1
+   :widths: 20 80 20
+
+   * - Define
+     - Description
+     - Default
+   * - ``XUA_NUM_PDM_MICS``
+     - The number of mics to enable (0 for disabled)
+     - ``0`` (disabled)
+   * - ``PDM_MIC_INDEX``
+     - Defines which input channel the mics map to 
+     - ``0``
+
+The codebase expects 1-bit ports to be defined in the application XN file for ``PORT_PDM_CLK`` and ``PORT_PDM_MCLK``.
+An 8-bit port is expected for ``PORT_PDM_DATA``. For example::
+
+    <Tile Number="0" Reference="tile[0]">
+        <!-- Mic related ports -->
+        <Port Location="XS1_PORT_1E" Name="PORT_PDM_CLK"/>
+        <Port Location="XS1_PORT_8B" Name="PORT_PDM_DATA"/>
+        <Port Location="XS1_PORT_1F" Name="PORT_PDM_MCLK"/>
+    </Tile>
+