drm/armada: Remove unused #include <drmP.h>

Remove drmP.h as it is not needed anymore since nothing it
defines is used in these files.

Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170927073846.GA14352@Haneen