driver core/ACPI: Introduce companion_bus_register()

The ACPI bus type does not allow drivers to be registered, so the sysfs
attributes related to drivers created for it and its devices are
useless, and its drivers/ directory is always empty.  All of that is
confusing and wasteful.

To allow skipping the creation of those sysfs attributes, introduce a
"companion" bus type concept and add a special registration function for
registering "companion" bus types, companion_bus_register().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://patch.msgid.link/6329043.lOV4Wx5bFT@rafael.j.wysocki
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>