drm/armada: replace the simple-framebuffer

If there's a simple-framebuffer carried over from boot firmware, it's going
to stop working once we setup the LCDC for use via DRM. Kick it off from
the hardware.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>