We currently have two schemes that try to ensure jitted code and statics
end up close to each other and close to coreclr. In Windows, we have
USE_UPPER_ADDRESS that lazily will reserve memory for loader heaps that
is close to coreclr. For PAL, we eagerly reserve a large chunk of memory
nearby during start up. However for PAL we were not using this region to
report back to the JIT that addresses in this range can use rip-relative
addressing. Add this support.

I have also cleaned up some of the code around USE_UPPER_ADDRESS: I have
renamed it to USE_LAZY_PREFERRED_RANGE and removed some dead code.