gpu: nvgpu: fix allocator debugfs deinit

Allocator (bitmap, buddy, page) debugfs files are not cleaned up when
the allocators are destroyed. This leads to warning logs from nvgpu
like below:

[21073.493000] debugfs: File 'gk20a_as_17' in directory 'allocators' already present!
[21073.493026] debugfs: File 'gk20a_as_17-sys' in directory 'allocators' already present!

Remove the per-allocator debugfs node when destroying an allocator in
runtime.

While at this, add missing nvgpu_allocator locking to the function
nvgpu_bitmap_alloc_destroy. And create nop functions for the
functions nvgpu_init_alloc_debug and nvgpu_fini_alloc_debug
when CONFIG_DEBUG_FS is not defined to avoid adding the
CONFIG checks at multiple places.

Move gk20a_debug_deinit to the end of gk20a_free_cb called in nvgpu_put
as that tears down all debugfs entries. Allocator destroy happens as
part of nvgpu_put call and it can lead to invalid debugfs dentry
access if gk20a_debug_deinit is called before it.

Bug 3481097

Change-Id: I8a66bcf6ade7e5707f9207c78a54d12d7bd94c02
Signed-off-by: Sagar Kamble <skamble@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2648012
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>

drivers/gpu/nvgpu/os/linux/module.c

@@ -1932,8 +1932,6 @@ int nvgpu_remove(struct device *dev)
 
 	gk20a_power_node_deinit(dev_from_gk20a(g));
 
-	gk20a_debug_deinit(g);
-
 	nvgpu_remove_sysfs(dev);
 
 	if (platform->secure_buffer.destroy)