drm/exynos: move exynos_drm_crtc and exynos_drm_fb defs to exynos_drm_drv.h

drm/exynos: move exynos_drm_crtc and exynos_drm_fb defs to exynos_drm_drv.h

Refactoring that is required for follow-up CLs. I need to access to
the crtc and fb struct from the finish_pageflip code called by the
vblank interrupt handler.

BUG=chrome-os-partner:12586
TEST=Suspend/resume. VT switch. Browsing.

Change-Id: Icb77eae4b10d481097abd4441d14d071f99a0e0e
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/30588
Reviewed-by: Pawel Osciak <posciak@google.com>