Some ECs need a little time for waking up before they can accept
SPI data at a high speed. Add a "google,cros-ec-spi-pre-delay"
property to the DT binding to configure this.

If this property isn't set, then no delay will be added. However,
if set it will cause a delay equal to the value passed to it to
be inserted at the beginning of a transaction.
Signed-off-by: NAlexandru M Stan <amstan@chromium.org>
Reviewed-by: NDoug Anderson <dianders@chromium.org>
Signed-off-by: NChris Zhong <zyw@rock-chips.com>
Signed-off-by: NJavier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: NHeiko Stuebner <heiko@sntech.de>
Acked-by: NLee Jones <lee.jones@linaro.org>
Acked-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NLee Jones <lee.jones@linaro.org>