Mark GPIO42 as unused according to Samus schematics
BUG=None
TEST=Make the chnage; Pass the build process; Need someone having
the board perform the verification.
Change-Id: Ifd6a0d2de8af0fe3af4a14f44ce572b41b77509c
Signed-off-by: Kenji Chen <kenji.chen@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/217344
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>