gpu: nvgpu: improve nvs uapi

- Make the domain scheduler timeslice type nanoseconds to future proof
  the interface
- Return -ENOSYS from ioctls if the nvs code is not initialized
- Return the number of domains also when user supplied array is present
- Use domain id instead of name for TSG binding
- Improve documentation in the uapi headers
- Verify that reserved fields are zeroed
- Extend some internal logging
- Release the sched mutex on alloc error
- Add file mode checks in the nvs ioctls. The create and remove ioctls
  require writable file permissions, while the query does not; this
  allows filesystem based access control on domain management on the
  single dev node.

Jira NVGPU-6788

Change-Id: I668eb5972a0ed1073e84a4ae30e3069bf0b59e16
Signed-off-by: Konsta Hölttä <kholtta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2639017
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: svc-mobile-cert <svc-mobile-cert@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit

include/uapi/linux/nvgpu.h

@@ -41,9 +41,10 @@ struct nvgpu_tsg_bind_channel_ex_args {
 };
 
 struct nvgpu_tsg_bind_scheduling_domain_args {
-	/* in: name of the domain this tsg will be bound to */
-	__u8 domain_name[16];
-	__u8 reserved[16];
+	/* in: id of the domain this tsg will be bound to */
+	__u64 domain_id;
+	/* Must be set to 0 */
+	__u64 reserved[3];
 };
 
 /*