samus: Disable SMBus controller

Nothing is connected to this port.

Change-Id: If3e466a3053fa694a511c2335c16381f77f56f47
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/174089
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
(cherry picked from commit 5ddb6a444d5c3141868eaf618ecb014b0262a796)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6827
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)