nouveau: add command-line GSP-RM registry support

Add the NVreg_RegistryDwords command line parameter, which allows
specifying additional registry keys to be sent to GSP-RM.  This
allows additional configuration, debugging, and experimentation
with GSP-RM, which uses these keys to alter its behavior.

Note that these keys are passed as-is to GSP-RM, and Nouveau does
not parse them.  This is in contrast to the Nvidia driver, which may
parse some of the keys to configure some functionality in concert with
GSP-RM.  Therefore, any keys which also require action by the driver
may not function correctly when passed by Nouveau.  Caveat emptor.

The name and format of NVreg_RegistryDwords is the same as used by
the Nvidia driver, to maintain compatibility.
Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240417215317.3490856-1-ttabi@nvidia.com

drivers/gpu/drm/nouveau/include/nvkm/subdev/gsp.h

@@ -211,6 +211,12 @@ struct nvkm_gsp {
 		struct mutex mutex;;
 		struct idr idr;
 	} client_id;
+
+	/* A linked list of registry items. The registry RPC will be built from it. */
+	struct list_head registry_list;
+
+	/* The size of the registry RPC */
+	size_t registry_rpc_size;
 };
 
 static inline bool