Mark cuttlefish_kernel_headers as vendor

Only vendor components can link to this.

Bug: 70485924
Test: $ lunch aosp_cf_x86_phone-userdebug; m -j
      $ lunch aosp_x86_64_ab-userdebug; m -j

Change-Id: I839d1ce2dae252c1f4c4cd6053bba7c8d0f9b79f