Enable TARGET_ARCH_LOWMEM for low memory targets

Change-Id: I07e5745ccb2acc9f02d4f06e25e1abc7115a7a26
Dalvik updates
- Configure dalvik heap parameters for low memory devices, ~512MB RAM or less (dalvik.vm.heaptargetutilization=0.25)
- Disable dalvik alloc debug output (dalvik.vm.debug.alloc=0)

Change-Id: Ic8cff0889edcc12807977e48bd28f20c94e3cb4f