Because CRAT_CU_FLAGS_IOMMU_PRESENT was not set in some BIOS crat, we
need to workaround this.

For future compatibility, we also overwrite the bit in capability according
to the value of needs_iommu_device.
Acked-by: NAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: NYong Zhao <Yong.Zhao@amd.com>
Reviewed-by: NFelix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: NFelix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>