drm/shmem-helper: Export dedicated wrappers for GEM object functions

Wrap GEM SHMEM functions for struct drm_gem_object_funcs and update
all callers. This will allow for an update of the public interfaces
of the GEM SHMEM helper library.

v2:
	* fix docs for drm_gem_shmem_object_print_info()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211108093149.7226-3-tzimmermann@suse.de