hw/nvram/fw_cfg: Remove fw_cfg_add_extra_pci_roots()

hw/nvram/fw_cfg: Remove fw_cfg_add_extra_pci_roots()

Now that all uses of fw_cfg_add_extra_pci_roots() have been
converted to the newer pci_bus_add_fw_cfg_extra_pci_roots(),
we can remove that bogus method. hw/nvram/fw_cfg must
stay generic. Device specific entries have to be implemented
using TYPE_FW_CFG_DATA_GENERATOR_INTERFACE.

This mostly reverts commit 0abd38885ac0fcdb08653922f339849cad387961
("fw_cfg: Refactor extra pci roots addition").

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20241206181352.6836-7-philmd@linaro.org>