QOM infrastructure fixes and device conversions

* Assertion fix for device_add with non-device types
* Documentation fix
* qdev_init() error reporting cleanups

# gpg: Signature made Tue Feb 24 13:56:33 2015 GMT using RSA key ID 3E7E013F
# gpg: Good signature from "Andreas Färber <afaerber@suse.de>"
# gpg:                 aka "Andreas Färber <afaerber@suse.com>"

* remotes/afaerber/tags/qom-devices-for-peter:
  parallel: parallel_hds_isa_init() shouldn't fail
  parallel: Factor out common parallel_hds_isa_init()
  serial: serial_hds_isa_init() shouldn't fail
  serial: Factor out common serial_hds_isa_init()
  etsec: Replace qdev_init() by qdev_init_nofail()
  leon3: Replace unchecked qdev_init() by qdev_init_nofail()
  ide/isa: Replace unchecked qdev_init() by qdev_init_nofail()
  qdev: Improve qdev_init_nofail()'s error reporting
  qom: Fix typo, 'my_class_init' -> 'derived_class_init'
  qdev: Avoid type assertion in qdev_build_hotpluggable_device_list()
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>