svm: improve fifo segment prealloc support

svm: improve fifo segment prealloc support

- track fifo segment free and chunk freelist memory
- improve fifo alloc. If there are enough chunks to satisfy a fifo
  allocation request but not enough free memory, allocate a multi-chunk
  fifo
- add apis to preallocate chunks and fifo headers
- more tests

Change-Id: If18dba7ab856272c9f565d36ac36365139793e0b
Signed-off-by: Florin Coras <fcoras@cisco.com>