rework HAL LInux coldplug to work with future kernel changes

[Artem Kachitchkine]

> In HAL, we must also get rid of properties in HAL like "*physical*" the
> "bus"-namespace and the sysfs_path_device keys. They all don't make any
> sense for userspace and are totally wrong in a virtualised environment.
> Devices will be just classified by their "subsystem" string.

Could you clarify, especially "bus" vs "subsystem"? We need common terminology 
to keep all HAL OSes (Linux, FreeBSD, Solaris) aligned. Some physical properties 
need to be there to, for instance, tell a USB disk from a FireWire disk.

-Artem.