drm/arc: Convert to drm_simple_kms_pipe_helper

Really straighforward, only slight issue is that the sim connector is
created after the pipe is set up, so can't use the helpers perfectly
yet. Subsequent patches will fix that.

Aside from lots of deleting code no functional changes in here.

v2: Delete now unused crtc funcs (0day)

v3: Move endcoder setup removal to right patch (Sam)

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210112084358.2771527-9-daniel.vetter@ffwll.ch