build: Add QCOM target-specific config

 * Needed to support global DirectTract config on legacy targets
 * Let's also eliminate some boilerplate

Change-Id: I736c10a5e7e1f3d1e0de9e60f29b60add276f151

Conflicts:
	core/config.mk
Merge branch 'kitkat' of github.com:AOSPA-legacy/android_build into kitkat-legacy