CHROMIUM: config: Remove duplicate CONFIG_RT2xxx

CHROMIUM: config: Remove duplicate CONFIG_RT2xxx

Fix-up entires so global chromeos/config/base.config entries
are all we need.

Signed-off-by: Paul Stewart <pstew@chromium.org>
BUG=chromium-os:36732,chromium-os:35699
TEST=emerge-{parrot,daisy,x86-alex} chromeos-kernel:
Ensure prepareconfig does not fail due to CONFIG_RT* (it fails in
all of these platforms but for other reasons than my changes)

Change-Id: I32be7178c5cf255392d9b015797b0a17cba5918f
Reviewed-on: https://gerrit.chromium.org/gerrit/38839
Tested-by: Grant Grundler <grundler@chromium.org>
Reviewed-by: Grant Grundler <grundler@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>