exynos: support DRM_IOCTL_EXYNOS_GEM_MAP

exynos: support DRM_IOCTL_EXYNOS_GEM_MAP

The commit d41b7a3a745a("exynos: Don't use DRM_EXYNOS_GEM_{MAP_OFFSET/
MMAP} ioctls") removed it same with the ioctl that this patch adds. The
reason that removed DRM_IOCTL_EXYNOS_GEM_MAP_OFFSET was we could use
DRM_IOCTL_MODE_MAP_DUMB. Both did exactly same thing.

Now exynos-drm driver of linux kernel revives it as DRM_EXYNOS_GEM_MAP
because of render node. DRM_IOCTL_MODE_MAP_DUMB isn't permitted in
render node, so this patch also supports DRM_IOCTL_EXYNOS_GEM_MAP.

Change-Id: Ib548dc8a6bea076375465f64ee2fdd658a90e435
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>