Build VNDK snapshot for products aosp_[arm|x86]

P VNDK snapshot needs to include VNDK libs built for 64-bit binder
products, aosp_arm and aosp_x86. This change modifies the following:

1) Revise VNDK snapshot zip file name to use $TARGET_PRODUCT instead of
$TARGET_ARCH in order to distinguish aosp_arm and aosp_arm_ab.
2) Place 32-bit binder libs under a subdirectory 'binder32' such that
the snapshots can be uploaded to prebuilts/vndk/v{VER} with the following
directory structure:

  prebuilts/vndk/v{VER}/
    arm/
      arch-arm-armv7-a-neon/
        shared/
          ...
      binder32/
        arch-arm-armv7-a-neon/
          shared/
            ...
      ...
    arm64/
      arch-arm-armv7-a-neon/
      arch-arm64-armv8-a/
      ...
    ...

The 32-bit binder libs will be placed in a separate subdirectory so that
they can be easily phased out in future VNDK snapshots.

Bug: 80372796
Test: make -j vndk dist
Merged-In: I7cde2e706e0c2891bab762b9057672f57e798873
Change-Id: I7cde2e706e0c2891bab762b9057672f57e798873
(cherry picked from commit 3ba44eb9)