Add ext_config feature to extend qcom's defconfig There make files can compose some kconfig files into one Change-Id: Ic1444100f61300e7ee16a81c73afde3dac81da0a Signed-off-by: zhaoxp3 <zhaoxp3@motorola.com> Reviewed-on: https://gerrit.mot.com/1499581 SLTApproved: Slta Waiver SME-Granted: SME Approvals Granted Tested-by: Jira Key Reviewed-by: Wang Wang <wangwang1@lenovo.com> Submit-Approved: Jira Key