hw/pci: Disable PCI_ERR_UNCOR_MASK register for machine type < 8.0

hw/pci: Disable PCI_ERR_UNCOR_MASK register for machine type < 8.0

Since it's implementation on v8.0.0-rc0, having the PCI_ERR_UNCOR_MASK
set for machine types < 8.0 will cause migration to fail if the target
QEMU version is < 8.0.0 :

qemu-system-x86_64: get_pci_config_device: Bad config data: i=0x10a read: 40 device: 0 cmask: ff wmask: 0 w1cmask:0
qemu-system-x86_64: Failed to load PCIDevice:config
qemu-system-x86_64: Failed to load e1000e:parent_obj
qemu-system-x86_64: error while loading state for instance 0x0 of device '0000:00:02.0/e1000e'
qemu-system-x86_64: load of migration failed: Invalid argument

The above test migrated a 7.2 machine type from QEMU master to QEMU 7.2.0,
with this cmdline:

./qemu-system-x86_64 -M pc-q35-7.2 [-incoming XXX]

In order to fix this, property x-pcie-err-unc-mask was introduced to
control when PCI_ERR_UNCOR_MASK is enabled. This property is enabled by
default, but is disabled if machine type <= 7.2.

Fixes: 010746ae1d ("hw/pci/aer: Implement PCI_ERR_UNCOR_MASK register")
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Leonardo Bras <leobras@redhat.com>
Message-Id: <20230503002701.854329-1-leobras@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1576
Tested-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>