qdev: rework device properties.

This patch is a major overhaul of the device properties.  The properties
are saved directly in the device state struct now, the linked list of
property values is gone.

Advantages:
  * We don't have to maintain the list with the property values.
  * The value in the property list and the value actually used by
    the device can't go out of sync any more (used to happen for
    the pci.devfn == -1 case) because there is only one place where
    the value is stored.
  * A record describing the property is required now, you can't set
    random properties any more.

There are bus-specific and device-specific properties.  The former
should be used for properties common to all bus drivers.  Typical
use case is bus addressing, i.e. pci.devfn and i2c.address.

Properties have a PropertyInfo struct attached with name, size and
function pointers to parse and print properties.  A few common property
types have PropertyInfos defined in qdev-properties.c.  Drivers are free
to implement their own very special property parsers if needed.

Properties can have default values.  If unset they are zero-filled.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>