staging: android: ion: Ensure ION supports concurrent CMO requests

ION userspace clients can request cache maintenance on an ION buffer at
any time using the DMA_BUF_IOCTL_SYNC IOCTL.

Ensure that the ION buffer is not in the process of being detached, dma
mapped or dma unmapped when client requested cache maintenance is carried
out.

Change-Id: I8d414af02dbfe8f6e81e0d518f9819b574a8da9f
Signed-off-by: Liam Mark <lmark@codeaurora.org>