edk2: Fix to get edk2 working for latest Android

According to platform/build/+/master/Changes.md, we shouldn't
rely on ANDROID_BUILD_TOP.

1. Replace deprecated ANDROID_BUILD_TOP with ANDROID_TOP which
   is the absolute path of the Android source (call pwd).
2. Use host tools from prebuilts.
3. Backward compatible with existing baselines.

Change-Id: I8b2a3131c09b82a8dbf14ff1c9a91eff3a6d93c0
2 files changed