drm/exynos: exynos_drm.h header file fixes

First of all #ifdef __KERNEL__ was added to exynos_drm.h to
mark the part that should be left out of userspace.
Secondly exynos_drm.h was added to include/drm/Kbuild, so it
will be included when doing make headers_install.

Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
diff --git a/include/drm/Kbuild b/include/drm/Kbuild
index a5c0e10..1e38a19 100644
--- a/include/drm/Kbuild
+++ b/include/drm/Kbuild
@@ -2,6 +2,7 @@
 header-y += drm_fourcc.h
 header-y += drm_mode.h
 header-y += drm_sarea.h
+header-y += exynos_drm.h
 header-y += i810_drm.h
 header-y += i915_drm.h
 header-y += mga_drm.h