misc: pmem: Add support for PMEM->ION wrapper.

PMEM to ION wrapper replaces standard PMEM driver with its own. It's sole
purpose is to redirect all PMEM allocations to ION.

If enabled, board driver must ensure pmem pdata provides .ion_heap_id with the
name of the ION heap ID (such as camera, mm, sf, etc).

Since some kernel drivers are PMEM based, all drivers that request PMEM memory
will be getting ION memory (get_pmem_file/put_pmem_file). On a corner case,
such as userspace allocating memory directly with /dev/ion, PMEM wrapper driver
will automatically import the fd (from PMEM id 0 ION client) and return the
memory from ION.

Not a complete solution. Unfinished features have been marked with TODO.

Currently unsupported commands:
flush_pmem_fd
flush_pmem_file

Currently unsupported ioctl commands:
PMEM_MAP
PMEM_UNMAP
PMEM_CONNECT
PMEM_GET_TOTAL_SIZE
PMEM_GET_FREE_SPACE

Change-Id: I507ce0850d6fdbac4a72c83105140e9f3992a678
Signed-off-by: Rudolf Tammekivi <rtammekivi@gmail.com>
Signed-off-by: Michael Bestas <mikeioannina@gmail.com>