drm/exynos: separate dpi from fimd

The patch separates dpi related routines from fimd.

Changelog v2:
- Rename ctx->dpi to ctx->display

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

diff --cc drivers/gpu/drm/exynos/exynos_drm_dpi.c
Simple merge

diff --cc drivers/gpu/drm/exynos/exynos_drm_drv.h
Simple merge

diff --cc drivers/gpu/drm/exynos/exynos_drm_fimd.c
Simple merge