LU-16724 ptlrpc: refactor page pools patch 3

LU-16724 ptlrpc: refactor page pools patch 3

This is a combined series that refactors the page pools
code to make it more readable.  It used to be many
separate patches but has been combined in to just three,
and this is the third of three.

LU-16724 ptlrpc: remove PAGES_PER_POOL macro

The page pool code *also* likes to refer to each page of
pointers it uses to track items in it as a "POOL", which is
incredibly confusing.

Start unwinding this by removing the PAGES_PER_POOL macro.

LU-16724 ptlrpc: change "pool" to "page_ptrs"

The page pool code *also* likes to refer to each page of
pointers it uses to track items in it as a "POOL", which is
incredibly confusing.

This patch works on renaming that to page_ptrs, but leaves
some steps for a future patch.

Change-Id-Was: I56ee54c7f39b52d7cceffec9e3decf71bd313ddc

LU-16724 ptlrpc: rename max_pools to max_ptr_pages

Continue removal of referring to page pointers as pools
with another rename.

Change-Id-Was: I14796f670a7f06fbec3b40ec23b4dd2e50f22d46

LU-16724 ptlrpc: rename npools to nptr_pages

Continue removal of 'pool' as a name for a page of pointers
to items in a pool.

Change-Id-Was: I97b320027a0a6b5870d246e1527fa3fbe15fccb5

LU-16724 ptlrpc: rename 'pools' to 'ptr_pages'

This finalizes the removal of the overloading of 'pools'
to also mean pointers of pages to items in each page pool.

Change-Id-Was: I0f4aba95f573f4afdc6f5d92f22fd67391fa6dab

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Ie29434f53eeb945b8d35df7c1212ae3f51a2aafa