vfio: Introduce a new header file for VFIOcontainer declarations

vfio: Introduce a new header file for VFIOcontainer declarations

Gather all VFIOcontainer related declarations into
"hw/vfio/vfio-container.h" to reduce exposure of VFIO internals in
"hw/vfio/vfio-common.h". These declarations were initially introduced
in commit 65501a745dba ("vfio: vfio-pci device assignment driver").
They are made available externally for PPC and s390x.

Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: John Levon <john.levon@nutanix.com>
Link: https://lore.kernel.org/qemu-devel/20250318095415.670319-12-clg@redhat.com
Link: https://lore.kernel.org/qemu-devel/20250326075122.1299361-13-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>