qdev-properties.c: Separate core from the code used only by qemu-system-*

qdev-properties.c: Separate core from the code used only by qemu-system-*

This separates the qdev properties code in two parts:
 - qdev-properties.c, that contains most of the qdev properties code;
 - qdev-properties-system.c for code specific for qemu-system-*,
   containing:
   - Property types: drive, chr, netdev, vlan, that depend on code that
     won't be included on *-user
   - qemu_add_globals(), that depends on qemu-config.o.

This change should help on two things:
 - Allowing DeviceState to be used by *-user without pulling
   dependencies that are specific for qemu-system-*;
 - Writing qdev unit tests without pulling too many dependencies.

The copyright/license of qdev-properties.c isn't explicitly stated at
the file, so add a simple copyright/license header pointing to the
commit ID of the original file.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>