drm/exynos: add iommu support for exynos drm framework

Changelog v4:
- fix condition to drm_iommu_detach_device funtion.

Changelog v3:
- add dma_parms->max_segment_size setting of drm_device->dev.
- use devm_kzalloc instead of kzalloc.

Changelog v2:
- fix iommu attach condition.
  . check archdata.dma_ops of drm device instead of
    subdrv device's one.
- code clean to exynos_drm_iommu.c file.
  . remove '#ifdef CONFIG_ARM_DMA_USE_IOMMU' from exynos_drm_iommu.c
    and add it to driver/gpu/drm/exynos/Kconfig.

Changelog v1:
This patch adds iommu support for exynos drm framework with dma mapping
api. In this patch, we used dma mapping api to allocate physical memory
and maps it with iommu table and removed some existing codes and added
new some codes for iommu support.

GEM allocation requires one device object to use dma mapping api so
this patch uses one iommu mapping for all sub drivers. In other words,
all sub drivers have same iommu mapping.

Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>