Use memory chunks for monitors on LP64

Monitor IDs in lock words are only 30b. On a 32b system that works
fine, as memory is usually aligned enough that shifting works out.
On 64b systems, the virtual memory space is too large for that.
This adds memory chunks into which we allocate the monitors so that
we have base_addr + offset and can use the offset as the monitor ID.
To allow for relatively compact but growable storage, we use a list
of chunks.

Added a global lock for the monitor pool.

Change-Id: I0e290c4914a2556e0b2eef9902422d7c4dcf536d