Some fixes and cleanup, mainly around fbdev emulation. It also adds a
new module parameter which allows to specify the color depth/bpp for
the fbdev emulation (like the IMX DRM driver).

* tag 'drm-fsl-dcu-for-next' of http://git.agner.ch/git/linux-drm-fsl-dcu:
  drm/fsl-dcu: introduce kernel parameter to specify fbdev depth
  drm/fsl-dcu: remove separate compilation unit for fbdev emulation
  drm/fsl-dcu: Propagate the real error code
  drm/fsl-dcu: Remove unneeded NULL check
  drm/fsl-dcu: disable outputs before unloading driver
  drm/fsl-dcu: unload driver before disabling clocks