If IOMMU_SUPPORT is not set, and COMPILE_TEST is y,
IOMMU_IOVA may be set to m. So building will fails:
drivers/staging/media/tegra-vde/iommu.o: In function `tegra_vde_iommu_map':
iommu.c:(.text+0x41): undefined reference to `alloc_iova'
iommu.c:(.text+0x56): undefined reference to `__free_iova'
Select IOMMU_IOVA while COMPILE_TEST is set to fix this.