Drop use of the deprecated header drmP.h.

Fix so header file became self-contained,
and then fixed fallout in the other files.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190630061922.7254-5-sam@ravnborg.org