hcq: use mmio interface in nv (#9986)

* hcq: start mmio interface

* allow double cast

* revert

* faster?

* simpler, not needed more now

* dd

* types

* fix

test/mockgpu/mockgpu.py

@@ -27,7 +27,7 @@ class TrackedMemoryView:
     self.wcb(self.mv, index)
 
   def cast(self, new_type, **kwargs):
-    self.mv = self.mv.cast(new_type, **kwargs)
+    self.mv = self.mv.cast('B').cast(new_type, **kwargs)
     return self
 
   @property