Expose memory tiers to command-line tools

[bgoglin]

hwloc-bind has --hbm and --no-hbm to filter HBMs in membind locations. This could be extended to hwloc-calc (both for input and output). And this should be extended to more than just HBM. We have some notion of memory tiers internally to detect what's DDR, HBM, NVM or SPM. Linux has some info too #576. We could use that in hwloc-bind and hwloc-calc , for instance for finding how the machine is divided by some sort of memory.

In the future, we could have an API to query memory tiers. But right now, a simple memory attribute in NUMA node, for instance MemoryTier=2 (value for the internal ranking of nodes based of performance) might be enough.

This internally memtier ranking envvar configuration could be extended, for instance if somebody wants to rank by latency instead of bandwidth. And it could even be overriden by an envvar such as HWLOC_MEMTIERS=HBM=0x0f;DDR=0xf;NVM=0x00f.

This will likely supersede the hwloc-calc part of #612.

[bgoglin]

This is fixed in master thanks to #630 and backported to 2.x