rk3288: Increase the delay after DDR reset de-assert to 10us.

After DDR PHY reset de-asserted, DLL automatically starts to
lock, and the lock time is maximum 5.12us. The output clock of
DLL supplies the clocks of DDR controller and PHY digital logic.
So before DLL lock, the clocks of DDR controller and PHY digital
logic are indeterminate. When programming DDR in the period of
DLL unlock, the programming maybe unstable because of the
indeterminate clocks. So we need wait for at least 5.12us after
de-asserting reset, then start to program DDR registers.
10us provide some safety margin.

BUG=chrome-os-partner:33148
TEST=I'm using the following command line test ok(15000 cycles).
"while sleep 4 && dut-control cold_reset:on sleep:.1 cold_reset:off;
do : ; done"
BRANCH=None

Change-Id: Ie7d615f5a2264c615c4b4413d6b828cd3d78cd2b
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Original-Commit-Id: 54e1a439c0e29aaf4fc542ae756f7bb036ceaf3e
Original-Change-Id: I55f8cb11ed3d7962567c5f40a31e6c8aed8fdcb0
Original-Signed-off-by: DaiLunXue <dlx@rock-chips.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/232894
Original-Reviewed-by: Julius Werner <jwerner@chromium.org>
Original-Commit-Queue: Lunxue Dai <lunxue.dai@rock-chips.com>
Original-Tested-by: Lunxue Dai <lunxue.dai@rock-chips.com>
Reviewed-on: http://review.coreboot.org/9578
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

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