hw/xen: Link XenPVH with GPEX PCIe bridge

hw/xen: Link XenPVH with GPEX PCIe bridge

XenPVH requires the PCIe/GPEX device. Add it to Kconfig
to avoid when configuring using --without-default-devices:

  /usr/bin/ld: libqemu-aarch64-softmmu.a.p/hw_xen_xen-pvh-common.c.o: in function `xenpvh_gpex_init':
  hw/xen/xen-pvh-common.c:174: undefined reference to `gpex_set_irq_num'
  /usr/bin/ld: libqemu-aarch64-softmmu.a.p/hw_xen_xen-hvm-common.c.o: in function `pci_dev_bus_num':
  include/hw/pci/pci.h:337: undefined reference to `pci_bus_num'
  /usr/bin/ld: include/hw/pci/pci.h:337: undefined reference to `pci_bus_num'
  /usr/bin/ld: include/hw/pci/pci.h:337: undefined reference to `pci_bus_num'
  /usr/bin/ld: include/hw/pci/pci.h:337: undefined reference to `pci_bus_num'
  /usr/bin/ld: include/hw/pci/pci.h:337: undefined reference to `pci_bus_num'
  /usr/bin/ld: libqemu-aarch64-softmmu.a.p/hw_xen_xen-hvm-common.c.o: in function `cpu_ioreq_config':
  hw/xen/xen-hvm-common.c:412: undefined reference to `pci_host_config_read_common'
  /usr/bin/ld: hw/xen/xen-hvm-common.c:428: undefined reference to `pci_host_config_read_common'
  /usr/bin/ld: hw/xen/xen-hvm-common.c:438: undefined reference to `pci_host_config_write_common'

Fixes: f22e598a72c ("hw/xen: pvh-common: Add support for creating PCIe/GPEX")
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Message-Id: <20250218162618.46167-2-philmd@linaro.org>