ipa: Move core IPA interface documentation to a .cpp file

Moving the core.mojom documentation to its corresponding .cpp file
(core_ipa_interface.cpp). This will allow Doxygen to generate the
documentation for IPABuffer, IPASettings and IPAStream structures.
Since the .mojom files are placed in include/ directory, the .cpp file
will live in $sourcedir/src/libcamera/ipa/ - which can also contain
documentation for other mojom generated IPA interfaces in subsequent
commit.

Also hide the constructors in generated IPA interface from doxygen,
via  #ifndef __DOXYGEN__. These constructors provide no major value in
documenting them, instead will spew out doxygen warnings during the
build.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Acked-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

utils/ipc/generators/libcamera_templates/definition_functions.tmpl

@@ -25,6 +25,7 @@ enum {{enum.mojom_name}} {
 struct {{struct.mojom_name}}
 {
 public:
+#ifndef __DOXYGEN__
 	{{struct.mojom_name}}() {%- if struct|has_default_fields %}
 		:{% endif %}
 {%- for field in struct.fields|with_default_values -%}
@@ -44,6 +45,8 @@ public:
 {%- endfor %}
 	{
 	}
+#endif
+
 {% for field in struct.fields %}
 	{{field|name}} {{field.mojom_name}};
 {%- endfor %}