malloc: enable memory hotplug support

malloc: enable memory hotplug support

This set of changes enables rte_malloc to allocate and free memory
as needed. Currently, it is disabled because legacy mem mode is
enabled unconditionally.

The way it works is, first malloc checks if there is enough memory
already allocated to satisfy user's request. If there isn't, we try
and allocate more memory. The reverse happens with free - we free
an element, check its size (including free element merging due to
adjacency) and see if it's bigger than hugepage size and that its
start and end span a hugepage or more. Then we remove the area from
malloc heap (adjusting element lengths where appropriate), and
deallocate the page.

For legacy mode, runtime alloc/free of pages is disabled.

It is worth noting that memseg lists are being sorted by page size,
and that we try our best to satisfy user's request. That is, if
the user requests an element from a 2MB page memory, we will check
if we can satisfy that request from existing memory, if not we try
and allocate more 2MB pages. If that fails and user also specified
a "size is hint" flag, we then check other page sizes and try to
allocate from there. If that fails too, then, depending on flags,
we may try allocating from other sockets. In other words, we try
our best to give the user what they asked for, but going to other
sockets is last resort - first we try to allocate more memory on
the same socket.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Tested-by: Santosh Shukla <santosh.shukla@caviumnetworks.com>
Tested-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Tested-by: Gowrishankar Muthukrishnan <gowrishankar.m@linux.vnet.ibm.com>