staging: drm/omap: use omapdss low level API

This patch changes the omapdrm KMS to bypass the omapdss "compat"
layer and use the core omapdss API directly.  This solves some layering
issues that would cause unpin confusion vs GO bit status, because we
would not know whether a particular pageflip or overlay update has hit
the screen or not.  Now instead we explicitly manage the GO bits in
dispc and handle the vblank/framedone interrupts ourself so that we
always know which buffers are being scanned out at any given time, and
so on.

As an added bonus, we no longer leave the last overlay buffer pinned
when the display is disabled, and have been able to add the previously
missing vblank event handling.

v1: original
v2: rebased on latest staging-next and omapdss patches from Tomi and
    review comments from Archit Taneja

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Archit Taneja <archit@ti.com>
Reviewed-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>