common-mk: Move Buffet out of platform2 ebuild.

Create a separate ebuild for Buffet.

BUG=chromium:407655
TEST=USE=buffet FEATURES emerge-link platform2
     USE=buffet FEATURES emerge-link buffet
CQ-DEPEND=CL:214221

Change-Id: Ibd5304a5184e7a768b0afcb17269a55f0928b280
Reviewed-on: https://chromium-review.googlesource.com/214244
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/common-mk/platform.gyp b/common-mk/platform.gyp
index f0a2ce2..9cc9af2 100644
--- a/common-mk/platform.gyp
+++ b/common-mk/platform.gyp
@@ -13,11 +13,6 @@
                 '<(DEPTH)/attestation/attestation.gyp:*',
               ],
             }],
-            ['USE_buffet == 1', {
-              'dependencies': [
-                '<(DEPTH)/buffet/buffet.gyp:*',
-              ],
-            }],
             ['USE_cellular == 1', {
               'dependencies': [
                 '<(DEPTH)/cromo/cromo.gyp:*',