CHROMIUM: drm/exynos: don't warn about non-kds modeset

CHROMIUM: drm/exynos: don't warn about non-kds modeset

Now that the page_flip logic is shared with the mode_set code,
it's possible for us to call page_flip on a non-kds buffer.
Modify the warning to only check the non-modeset case.

BUG=chrome-os-partner:15349,chrome-os-partner:14965
TEST=dmesg | grep non-kds

Change-Id: I2c23900fffd565886dcccf0e2b79fd04c1b0ab64
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/39385
Reviewed-by: Simon Que <sque@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>