Align generators/generator/gpdsc description in doc to XSD schema (#316)

The `generators/generator/gpdsc` element has `type = xs:string` in the
documentation while it has `type = GpdscFileType` in the Pack.xsd schema
(with `GpdscFileType` that has an attribute `name = xs:string`).

In this PR I've aligned the description in the documentation to what is
defined in the schema.

---------

Signed-off-by: Silvio Lucio Oliva <silvio.oliva@st.com>
Co-authored-by: Joachim Krech <joachim.krech@arm.com>

doxygen/src/generators_schema.txt

@@ -253,12 +253,12 @@ generator element must exist.
     <td>0..1</td>
   </tr>
   <tr>
-    <td>gpdsc</td>
+    <td>\ref element_gen_gpdsc "gpdsc"</td>
     <td>Path and name of the GPDSC that the generator creates and updates. The path is either absolute or relative to the
 	    working directory. If no explicit gpdsc file is provided, then a gpdsc file named after the project with extension gpdsc in
 		the working directory is assumed (\c \<project>.gpdsc).
     </td>
-    <td>xs:string</td>
+    <td>GpdscFileType</td>
     <td>0..1</td>
   </tr>
   <tr>
@@ -307,7 +307,7 @@ generator element must exist.
 \section element_gen_select /package/generators/generator/select
 
 This element contains information about the vendor and device the GPDSC file has been generated for. Only one such
-element can exist in \c \<generators>.
+element can exist in \ref element_generator "\<generator>".
 
 \b Example:
 \code
@@ -364,6 +364,49 @@ element can exist in \c \<generators>.
 <p>&nbsp;</p>
 <hr>
 
+\section element_gen_gpdsc /package/generators/generator/gpdsc
+
+Path and name of the GPDSC that the generator creates and updates. 
+The path is either absolute or relative to the working directory. 
+If no explicit gpdsc file is provided, then a gpdsc file named after the project with extension gpdsc in the working directory is assumed (\<project>.gpdsc).
+Only one such element can exist in \ref element_generator "\<generator>".
+
+\b Example:
+\code
+  <generators>
+    <generator id="MyGen">
+      <gpdsc name="$P/RTE/MyGen/myGen.gpdsc"/>
+    </generator>
+  </generators>
+\endcode
+<p>&nbsp;</p>
+
+<table class="cmtable" summary="Element: Generator Gpdsc">
+  <tr>
+    <th>Parent</th>
+    <th colspan="3">Chain</th>
+  </tr>
+  <tr>
+    <td>\ref element_generator "generator"</td>
+    <td colspan="3">\ref element_generator</td>
+  </tr>
+  <tr>
+    <th>Attributes</th>
+    <th>Description</th>
+    <th>Type</th>
+    <th>Use</th>
+  </tr>
+  <tr>
+    <td>name</td>
+	<td>Path and name of the GPDSC that the generator creates and updates.
+	</td>
+	<td>xs:string</td>
+	<td>required</td>
+  </tr>
+</table>
+<p>&nbsp;</p>
+<hr>
+
 \section element_gen_exe /package/generators/generator/exe
 
 This element contains information about the generation binary/executable.