REORG: memory: move the pool type definitions to haproxy/pool-t.h

This is the beginning of the move and cleanup of memory.h. This first
step only extracts type definitions and basic macros that are needed
by the files which reference a pool. They're moved to pool-t.h (since
"pool" is more obvious than "memory" when looking for pool-related
stuff). 3 files which didn't need to include the whole memory.h were
updated.
5 files changed