drm/exynos: Remove Kconfig deps for FIMD and DECON7

While the Kconfig entries of FIMD and DECON7 both select
FB_MODE_HELPERS, the code doesn't use any of the functionality.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1484928172-16784-1-git-send-email-tjakobi@math.uni-bielefeld.de