exynos: remove DRM_EXYNOS_GEM_{MAP_OFFSET/MMAP} ioctls

This patch removes the ioctls which are removed from the linux kernel.

Signed-off-by: Hyungwon Hwang <human.hwang@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Rob Clark <robclark@freedesktop.org>