drm/msm: Remove struct msm_fbdev

drm/msm: Remove struct msm_fbdev

Remove struct msm_fbdev, which is an empty wrapper around struct
drm_fb_helper. Use the latter directly. No functional changes.

v2:
	* kfree fbdev helper instance on init errors (Dmitri)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/530554/
Link: https://lore.kernel.org/r/20230403124538.8497-5-tzimmermann@suse.de
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>