cores/video/VideoTimingGenerator: Allow passing custom dict as default_video_timings.

Allow only listing the classical video timings in the core and let user provide the timings
specific to other configurations.

litex/soc/cores/video.py

@@ -152,14 +152,17 @@ video_data_layout = [
 
 class VideoTimingGenerator(Module, AutoCSR):
     def __init__(self, default_video_timings="800x600@60Hz"):
-        # Check / Get Video Timings.
-        try:
-            self.video_timings = vt = video_timings[default_video_timings]
-        except KeyError:
-            msg = [f"Video Timings {default_video_timings} not supported, availables:"]
-            for video_timing in video_timings.keys():
-                msg.append(f" - {video_timing} / {video_timings[video_timing]['pix_clk']/1e6:3.2f}MHz.")
-            raise ValueError("\n".join(msg))
+        # Check / Get Video Timings (can be str or dict)
+        if isinstance(default_video_timings, str):
+            try:
+                self.video_timings = vt = video_timings[default_video_timings]
+            except KeyError:
+                msg = [f"Video Timings {default_video_timings} not supported, availables:"]
+                for video_timing in video_timings.keys():
+                    msg.append(f" - {video_timing} / {video_timings[video_timing]['pix_clk']/1e6:3.2f}MHz.")
+                raise ValueError("\n".join(msg))
+        else:
+            self.video_timings = vt = default_video_timings
 
         # MMAP Control/Status Registers.
         self._enable      = CSRStorage(reset=1)