drm/scheduler: drop use of drmP.h

Drop use of the deprecated drmP.h header file.
Fix fallout.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: Sharat Masetty <smasetty@codeaurora.org>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Nayan Deshmukh <nayan26deshmukh@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190630061922.7254-26-sam@ravnborg.org