spapr-tce: make sPAPRTCETable a proper device

Model TCE tables as a device that's hooked up as a child object to
the owner.  Besides the code cleanup, we get a few nice benefits:

1) free actually works now (it was dead code before)

2) the TCE information is visible in the device tree

3) we can expose table information as properties such that if we
   change the window_size, we can use globals to keep migration
   working.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-id: 1374175984-8930-6-git-send-email-aliguori@us.ibm.com
[dwg: pseries: savevm support for PAPR TCE tables]
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[alexey: ppc kvm: fix to compile]
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
