Revert "drm/exynos: implement an optimized page_flip"

Revert "drm/exynos: implement an optimized page_flip"

This reverts commit 69518a3c650de9186f345a5e7feaddbadfc394d0.

We want to be able to call page_flip from mode_set and mode_set_base
so that all functions which cause a buffer to be scanned out are
synchronized.

BUG=chrome-os-partner:15349,chrome-os-partner:14965
TEST=Multiple VT switch, HDMI plug/unplug, sign in/out, suspend/resume,
     idle suspend/resume.

Change-Id: I198962b65bb8a1ab5b885c053c19f7f8077cb9c6
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/37571