drm/exynos: removed optional dummy encoder mode_fixup function.

drm/exynos: removed optional dummy encoder mode_fixup function.

mode_fixup function for encoder drivers became optional with patch
http://patchwork.freedesktop.org/patch/msgid/1455106522-32307-1-git-send-email-palminha@synopsys.com

This patch set nukes all the dummy mode_fixup implementations.

(made on top of Daniel topic/drm-misc branch)

Signed-off-by: Carlos Palminha <palminha@synopsys.com>
[danvet: Squash in 2nd exynos patch.]
Link: http://patchwork.freedesktop.org/patch/msgid/3768b670931572de51fca1102efa18d20dd770ee.1455540137.git.palminha@synopsys.com
Link: http://patchwork.freedesktop.org/patch/msgid/4906a9925eebbe55489b1005c449b426a61c09bd.1455540137.git.palminha@synopsys.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>