(RVA_TO_PTR): Redefine to convert RVA to address in

(RVA_TO_PTR): Redefine to convert RVA to address in
current process.
(round_to_next): Obsolete function removed.
(preload_heap_section): New variable.
(data_region_size): Obsolete variable removed.
(allocate_heap): Modified to determine end of static heap section
used during preload, and use that as initial base address for
dynamic heap instead of hard-coded value.
(sbrk): Remove call to allocate_heap; handled by init_heap.  Skip
calls to commit or decommit pages when allocating from static heap
section during preload.
(recreate_heap): Obsolete function removed.
(init_heap): New function to initialize internal sbrk heap
variables.  Uses static heap section during preload, otherwise
calls allocate_heap to reserve a heap region dynamically.
(round_heap): Use ROUND_UP macro instead of round_to_next.