drm/vc4: Add create and map BO ioctls.

While there exist dumb APIs for creating and mapping BOs, one of the
rules is that drivers doing 3D acceleration have to provide their own
APIs for buffer allocation (besides, the pitch/height parameters of
the dumb alloc don't really make sense for a lot of 3D allocations).

v2: Use __u32-style types, use "drm.h" instead of <drm/drm.h>.

Signed-off-by: Eric Anholt <eric@anholt.net>