mem: add length to memseg list

mem: add length to memseg list

Previously, to calculate length of memory area covered by a memseg
list, we would've needed to multiply page size by length of fbarray
backing that memseg list. This is not obvious and unnecessarily
low level, so store length in the memseg list itself.

This breaks ABI, so bump the EAL ABI version and document the
change. Also, while we're breaking ABI, pack the members a little
better.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Shreyansh Jain <shreyansh.jain@nxp.com>