gpu: nvgpu: Put debugfs dependencies inside #ifdef

Put all debugfs dependencies inside #ifdef CONFIG_DEBUG_FS. This
includes some functions in allocators that were used only for
debugging.

Remove include of linux/debugfs.h on files that do not deal with
debugfs.

linux/debugfs.h implicitly included linux/fs.h, which we relied on.
Add explicit include of linux/fs.h for all files where this is the
case.

Change-Id: I16feffae6b0e3a2edf366075cdc01ade86be06f9
Signed-off-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-on: http://git-master/r/1467897
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit

drivers/gpu/nvgpu/common/linux/ioctl_ctrl.c

@@ -18,6 +18,7 @@
 #include <linux/cdev.h>
 #include <linux/file.h>
 #include <linux/anon_inodes.h>
+#include <linux/fs.h>
 #include <uapi/linux/nvgpu.h>
 
 #include <nvgpu/bitops.h>