vfio/iommufd: Save vendor specific device info

vfio/iommufd: Save vendor specific device info

Some device information returned by ioctl(IOMMU_GET_HW_INFO) are vendor
specific. Save them as raw data in a union supporting different vendors,
then vendor IOMMU can query the raw data with its fixed format for
capability directly.

Because IOMMU_GET_HW_INFO is only supported in linux, so declare those
capability related structures with CONFIG_LINUX.

Suggested-by: Eric Auger <eric.auger@redhat.com>
Suggested-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250604062115.4004200-5-zhenzhong.duan@intel.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>