Use Ashmem to reduce buffer copies

Use android.os.MemoryFile to allocate Ashmem and use gsid.setAshmem and
gsid.commitGsiChunkFromAshmem to submit data.

Bug: 138976291
Test: adb shell am start-activity \
    -n com.android.dynsystem/com.android.dynsystem.VerificationActivity \
    -a android.os.image.action.START_INSTALL \
    -d file:///storage/emulated/0/Download/system.raw.gz \
    --el KEY_SYSTEM_SIZE $(du -b system.raw|cut -f1) \
    --el KEY_USERDATA_SIZE 8589934592

Change-Id: I6df718a8cc3f4e5835c9d20d0bf5bf8bb0daee22
Merged-In: I6df718a8cc3f4e5835c9d20d0bf5bf8bb0daee22