mempool: Rename pool policy

mempool: Rename pool policy

Rename pool policy from:

RSEQ_MEMPOOL_POPULATE_PRIVATE_NONE -> RSEQ_MEMPOOL_POPULATE_COW_INIT
RSEQ_MEMPOOL_POPULATE_PRIVATE_ALL -> RSEQ_MEMPOOL_POPULATE_COW_ZERO

to make it clear to the user that the COW_ZERO pool policy benefits from
leaving the memory zero-allocated.

Also, now that zmalloc checks the prior content for zero to prevent
useless COW of the per-cpu ranges, the term "populate all" does not fit
well anymore. Copy-on-write from the zero page is clearer.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: If97984225d971a2f48ba241b2a9570e81079bd03