M2: ion: ioctl compatibility with userland using old api

As far as I can tell, flags passed by userland are now used to determine
buffer caching.

Note in ION_IOC_ALLOC_COMPAT we are currently forcing uncached buffer
allocations (needed to make a choice here).  This
may need to change.
M2: ion: using client->heap_mask instead of ion_full_heap_mask in COMPAT ioctl