mem: improve segment list preallocation

mem: improve segment list preallocation

Current code to preallocate segment lists is trying to do
everything in one go, and thus ends up being convoluted,
hard to understand, and, most importantly, does not scale beyond
initial assumptions about number of NUMA nodes and number of
page sizes, and therefore has issues on some configurations.

Instead of fixing these issues in the existing code, simply
rewrite it to be slightly less clever but much more logical, and
provide ample comments to explain exactly what is going on.

We cannot use the same approach for 32-bit code because the
limitations of the target dictate current socket-centric
approach rather than type-centric approach we use on 64-bit
target, so 32-bit code is left unmodified. FreeBSD doesn't
support NUMA so there's no complexity involved there, and thus
its code is much more readable and not worth changing.

Fixes: 1d406458db47 ("mem: make segment preallocation OS-specific")
Cc: stable@dpdk.org
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>