CHROMIUM: chromeos platform: ramoops OF fix

CHROMIUM: chromeos platform: ramoops OF fix

Removes a warning at boot time due to multiple calls; once when
the platform_device is registered, another when the of-probed version
comes along.

Skip the regular platform device when OF is enabled.

BUG=none
TEST=boot, check for warnings.

Change-Id: I7d9edf9bf91342a5e1f5ab8bf3a489ffd355c2d3
Signed-off-by: Olof Johansson <olofj@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28245
Reviewed-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Reviewed-by: Bryan Freed <bfreed@chromium.org>