rockchip: rk3399: provide multiple SDRAM configuratinons

We want to be able to easily change SDRAM clock rate for debugging
purposes. This patch adds configurations for 4 different clock rates.

Same configs are used for all rk3399 boards at 200, 666 and 800 MHz.
Kevin board does not run reliably at 666 MHz, an option for it is
added to run at 300 MHz, this option is available to Kevin only.

There is not much room left in the coreboot romstage section, this is
why the config file for 928 MHz is being added with this patch but is
not included in the code, one of the lower frequency options will have
to be dropped for the higher frequency option to be added.

BRANCH=none
BUG=chrome-os-partner:54144
TEST=run "stressapptest -M 1024 -s 3600" and pass on both kevin and
     gru. Verified that on Kevin the firmware reports starting up
     SDRAM at 300 MHz and on Gru - at 800 MHz.

Change-Id: I08bccd40147ad89d851b995a8aab4d2b6da8258a
Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/353493
Reviewed-by: Derek Basehore <dbasehore@chromium.org>
5 files changed