i386/pc: pass pci_hole64_size to pc_memory_init()

Use the pre-initialized pci-host qdev and fetch the
pci-hole64-size into pc_memory_init() newly added argument.
Use PCI_HOST_PROP_PCI_HOLE64_SIZE pci-host property for
fetching pci-hole64-size.

This is in preparation to determine that host-phys-bits are
enough and for pci-hole64-size to be considered to relocate
ram-above-4g to be at 1T (on AMD platforms).

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20220719170014.27028-4-joao.m.martins@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>