Revert "Revert "emulator: create qemu images for system,vendor""

This reverts commit 9b99ddc8a58fc54c04a74b4a158bc06b90420f02.
and add syste-qemu.img to the dependency list of sdk target

Test: build sdk target successfully

Change-Id: Idb0bee56275f3bfe33ba7d29463e4b8e0699ec33
8 files changed