Prepare dir structure for multi-arch prebuilts.

The change is currently a no-op. The prebuilts directories contain
copies of the currently available prebuilts (x86). A new drop of
prebuilts will follow in a separate CL.

The Android.bp was modified with the following command:
sed -i -E 'sA  src: "testdata/apex/(.+)"A  arch: {\n        arm: {\n              src: "testdata/apex/arm/\1",\n        },\n        arm64: {\n              src: "testdata/apex/arm/\1",\n        },\n        x86: {\n              src: "testdata/apex/x86/\1",\n        },\n        x86_64: {\n              src: "testdata/apex/x86/\1",\n        },\n    }Ag' Android.bp

Bug: 148489495
Test: mm
Change-Id: Ie99a7784fc10c4501d1a30a94bf80cd2941a3394
35 files changed