The EC has specific timing it requires. Add support for an optional delay
after raising CS to fix timing issues. This is configurable based on
a DT property "google,cros-ec-spi-msg-delay".

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 end of a transaction.
Signed-off-by: NRhyland Klein <rklein@nvidia.com>
Reviewed-by: NBernie Thompson <bhthompson@chromium.org>
Reviewed-by: NAndrew Bresticker <abrestic@chromium.org>
Acked-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>