drm/exynos: Refactor manager/display/overlay

drm/exynos: Refactor manager/display/overlay

The exynos_drm_manager/display/overlay architecture wasn't really
serving its purpose. It attempted to split callbacks into logical
sections, but those sections didn't really make sense, and required us
to have a layer of abstraction such as exynos_drm_hdmi on top of the
controller and panel to call the appropriate functions.

This patch removes manager/display/overlay as well as exynos_drm_hdmi,
and adds a new abstraction which splits the callbacks to controller and
panel.

Right now, this just cleans things up, making the code a little more
readable. In the short term, it allows us to hook fimd into just
the controller side, and add dp/mipi as panel implementations. In the
long term, it removes all of the device pointers, so we should be able
to remove all of the various platform drivers more easily.

BUG=chrome-os-partner:11158,chrome-os-partner:10717
TEST=Tested on snow, hdmi hotplugged, booted with/without hdmi,
suspend/resume tested. No regressions detected.

Change-Id: Ia1bd6bbd67d49af2abecf36c43bfe765ae00f38d
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/36477
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>