This change adds support function to add STA function which returns an external variable. Change-Id: I31755a76ee985ee6059289ae194537d531270761 Signed-off-by: Sugnan Prabhu S <sugnan.prabhu.s@intel.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/42245 Reviewed-by: Rizwan Qureshi <rizwan.qureshi@intel.com> Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org> Tested-by: build bot (Jenkins) <no-reply@coreboot.org>