drm/exynos: use driver internal struct

drm/exynos: use driver internal struct

Use driver internal struct as argument instead of struct exynos_drm_crtc
except functions of exynos_drm_crtc_ops and instead of struct
exynos_drm_display except functions of exynos_drm_display_ops.

It can reduce unnecessary variable declaration.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>