drm/gma500: drop drmp.h include from all .c files

Drop remaining uses of the deprecated drmP.h in gma500

Replaced drmp.h with forward declarations or include files
as relevant.

Moved all include files to blocks in following order:
\#include <linux/*>

\#include <asm/*>

\#include <drm/*>

\#include ""

And within each block sort the include files alphabetically.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190519195526.3422-6-sam@ravnborg.org