drm/shmem: drop DEFINE_DRM_GEM_SHMEM_FOPS

DEFINE_DRM_GEM_SHMEM_FOPS is identical
to DEFINE_DRM_GEM_FOPS now, drop it.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20191016115203.20095-6-kraxel@redhat.com