CHROMIUM: ARM: exynos: snow: Turn down drive strength for wifi pins

CHROMIUM: ARM: exynos: snow: Turn down drive strength for wifi pins

We are seeing EMI from the SDIO clock on Snow.  Turn down the drive
strength of these pins to reduce hard edges on the lines and improve
EMI.  We're not adjusting Daisy settings right now since WiFi is hooked
up differently there and we need extra testing to tell that the drive
strength is safe.

BUG=chrome-os-partner:12151
TEST=Boot on Snow and see WiFi still work.
TEST=Measure EMI and see it reduced.  After applying that CL, EMI is
lower than before(5dB lower at 450MHz/11dB lower at 750MHz).
TEST=Ran wifi test suites (MatFunc, Manager, SecMat) and didn't see
any instability which could be introduced by this CL

Change-Id: Ib979a57710117edc60893c0d32f5b64eeb6cc6db
Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/29084
Reviewed-by: Tan Gao <tgao@chromium.org>