kdbus: add driver skeleton, ioctl entry points and utility functions

kdbus: add driver skeleton, ioctl entry points and utility functions

Add the basic driver structure.

handle.c is the main ioctl command dispatcher that calls into other parts
of the driver.

main.c contains the code that creates the initial domain at startup, and
util.c has utility functions such as item iterators that are shared with
other files.

limits.h describes limits on things like maximum data structure sizes,
number of messages per users and suchlike. Some of the numbers currently
picked are rough ideas of what what might be sufficient and are probably
rather conservative.

Change-Id: I48b15c95f89f24bad0287be5aad2ac18e3e70326
Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Osmialowski <p.osmialowsk@samsung.com>