Split common.mk product definitions into base.mk (shared between
32-bit and 64-bit targets) and common64.mk (64-bit targets).
common.mk is then for 32-bit only targets.
32-bit MSM target will inherit common.mk (no change to existing
MSM target definitions), whereas new 64-bit targets will inherit
common64.mk
Change-Id: I968be0e6b7077083bacddd3d163a4406f9b0c2f3
David Ng