exynos: Don't use DRM_EXYNOS_GEM_{MAP_OFFSET/MMAP} ioctls

The ioctl DRM_EXYNOS_GEM_MAP_OFFSET and DRM_EXYNOS_GEM_MMAP are removed from
the linux kernel. This patch modifies libdrm and libkms to use drm generic
ioctls instead of the removed ioctls.

v2: The original patch was erroneous. In case the MODE_MAP_DUMB ioctl failed
    it would return the retvalue as a void-pointer. Users of libdrm would then
    happily use that ptr, eventually leading to a segfault. Change this to
    return NULL in that case and also restore the previous behaviour of logging
    to stderr.
    The other error was that 'bo->vaddr' was never filled with the mapped
    buffer address. Hence exynos_bo_map still returned NULL even if the
    buffer mapping succeeded.

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>