drm/armada: drop use of drmP.h

Drop use of the deprecated drmP.h header file.
While touching the list of include files group them and sort them.
Fix fallout from the header file removal.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190804094132.29463-4-sam@ravnborg.org