gpu_usage: Initial import of script to read gpu usage debugfs info

Shows gpu usage as reported by the v3d driver.
Works on pi4 and pi5 (earlier models don't expose this info)

This provides a little more detail than the GPU taskbar plugin
(which just reports the maximum of the different fields).

scripts/gpu_usage.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python3
+
+import time
+import operator
+
+def get_stats():
+  try:
+    with open('/sys/kernel/debug/dri/0/gpu_usage') as f:
+      lines = f.readlines()
+  except:
+    print("gpu_uage is not supported on this device")
+    exit(1)
+  queue = {}
+  for i in lines:
+    s = i.replace("'", "").replace('"', "").strip().rstrip(';').split(';')
+    queues = ["bin", "render", "tfu", "csd", "cache_clean"]
+    if s[0] == 'timestamp':
+        timestamp = int(s[1])
+    elif s[0] == 'QUEUE':
+        names = s[1:]
+    elif s[0].replace("v3d_", "") in queues:
+        queue[s[0]] = list(map(int, s[1:]))
+    else:
+        print(s)
+        assert(False)
+  return timestamp, names, queue
+
+last_timestamp = None
+
+while True:
+  timestamp, names, queue = get_stats()
+  if last_timestamp is not None:
+    q = {}
+    t = timestamp - last_timestamp
+    for k,v in queue.items():
+      q[k] = list(map(operator.sub, queue[k], last_queue[k]))
+    s = []
+    for k,v in q.items():
+      s.append(f"{k}: jobs:{v[0]:3}{100.0*v[1]/t:6.1f}%")
+    print(", ".join(s))
+  last_timestamp = timestamp
+  last_queue = queue
+  time.sleep(1)