drm/fb-helper: Move out commit code

Move the modeset commit code to drm_client_modeset.
No changes except exporting API.

v7: Export drm_client_panel_rotation() (Gerd Hoffmann)
v2: Move to drm_client_modeset.c instead of drm_client.c

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190531140117.37751-5-noralf@tronnes.org


Patch-mainline: 20190531140117.37751-5-noralf@tronnes.org @ 31/05/19, 02:01 p.m.
[stalek@codeaurora.org:
1. drop changes for drm_fb_helper.c, since it is not require.
2. drop inclusion of drm_drv.h header file as it is not present.
3. drop changes related to panel rotation.].

Change-Id: I081430186fd88f1cdf606a28633c4304c312897e
Signed-off-by: Shubham Talekar <stalek@codeaurora.org>