Bluetooth: Convert debug files to actually use debugfs instead of sysfs

Some of the debug files ended up wrongly in sysfs, because at that point
of time, debugfs didn't exist. Convert these files to use debugfs and
also seq_file. This patch converts all of these files at once and then
removes the exported symbol for the Bluetooth sysfs class.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>