rust: miscdevice: add fops->show_fdinfo() hook

File descriptors should generally provide a fops->show_fdinfo() hook for
debugging purposes. Thus, add such a hook to the miscdevice
abstractions.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20241203-miscdevice-showfdinfo-v1-1-7e990732d430@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>