Link drm_fb_cma_helper.o into drm_cma_helper.ko if CONFIG_DRM_KMS_HELPER
has been set. Remove CONFIG_DRM_KMS_CMA_HELPER config option. Selecting
KMS helpers and CMA will now automatically enable CMA KMS helpers.

Some drivers' Kconfig files did not correctly select KMS or CMA helpers.
Fix this as part of the change.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211106193509.17472-3-tzimmermann@suse.de