gralloc: Support allocate buffer without import

Media allocates buffers but doesn't import until they absolutely
need to. In order to support codec2 moving to GraphicBufferAllocator,
add a function that allows them to allocate without import.

Bug: 145139476
Test: VtsHalMediaC2V1_0Host &&
    cherry pick ag/9741096 and run
    android.media.cts.MediaMetadataRetrieverTest#testThumbnailVP9Hdr

Change-Id: Icbd5943d45f20cb796204f816e5aac446d402979