mmc: sunxi: Support controllers that can use both old and new timings

On the SoCs that introduced the new timing mode for MMC controllers,
both the old (where the clock delays are set in the CCU) and new
(where the clock delays are set in the MMC controller) timing modes
are available, and we have to support them both. However there are
two bits that control which mode is active. One is in the CCU, the
other is in the MMC controller. The settings on both sides must be
the same, or nothing will work.

The sunxi-ng clock driver provides an API to query and set the
active timing mode. At probe time, we try to set the active mode
to the "new timing mode". If it succeeds, we can then use the MMC
controller in the new mode. If not, we fall back to the old mode.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>