meta-g220a: Support gatesgarth

The upstream is updated to support Yocto gatesgarth tag, fix the
meta-g220a layer:
* Remove meta-x86 which is empty and does not support gatesgarth yet;
* Add gatesgarth in meta-g220a layer.

Tested: Verify meta-g220a builds fine with upstream code.

(From meta-bytedance rev: 5ba67f07bc7d145712d56eaa70d892cb8ba9fc3e)

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I98eebe6472dccf88837df23de7b4f8f757d64f19
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>