drm/exynos: drop use of drmP.h

drm/exynos: drop use of drmP.h

There was a few uses of drmP that was missed in the last
patch removing this header from exynos.

Remove the final uses of this header.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Joonyoung Shim <jy0922.shim@samsung.com>
Cc: Seung-Woo Kim <sw0312.kim@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Kukjin Kim <kgene@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>