[Bluetooth] Consolidate maintainers information

The Bluetooth entries for the MAINTAINERS file are a little bit too
much. Consolidate them into two entries. One for Bluetooth drivers and
another one for the Bluetooth subsystem.

Also the MODULE_AUTHOR should indicate the current maintainer of the
module and actually not the original author. Fix all Bluetooth modules
to provide current maintainer information.

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