gpu: host1x: select IOMMU_IOVA

When IOMMU_IOVA is not built-in but host1x is, we get a link error:

drivers/gpu/host1x/dev.o: In function `host1x_remove':
dev.c:(.text.host1x_remove+0x50): undefined reference to `put_iova_domain'
drivers/gpu/host1x/dev.o: In function `host1x_probe':
dev.c:(.text.host1x_probe+0x31c): undefined reference to `init_iova_domain'
dev.c:(.text.host1x_probe+0x38c): undefined reference to `put_iova_domain'
drivers/gpu/host1x/cdma.o: In function `host1x_cdma_init':
cdma.c:(.text.host1x_cdma_init+0x238): undefined reference to `alloc_iova'
cdma.c:(.text.host1x_cdma_init+0x2c0): undefined reference to `__free_iova'
drivers/gpu/host1x/cdma.o: In function `host1x_cdma_deinit':
cdma.c:(.text.host1x_cdma_deinit+0xb0): undefined reference to `free_iova'

This adds the same select statement that we have for drm_tegra.

Fixes: 404bfb78 ("gpu: host1x: Add IOMMU support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170419182449.885312-1-arnd@arndb.de