media: staging: tegra-vde: Fix build error

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.

Reported-by: Hulk Robot <hulkci@huawei.com>
Suggested-by: Dmitry Osipenko <digetx@gmail.com>
Fixes: b301f8de ("media: staging: media: tegra-vde: Add IOMMU support")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>