pvmfw: Prepare heap.rs for move

Allow client code to control the size of the HEAP through a macro.

Make the SAFETY comment a compliant docstring.

Test: TH
Change-Id: I386e0c2e070e8c96f90560881005af827607fecc
diff --git a/vmbase/src/memory/mod.rs b/vmbase/src/memory/mod.rs
index 9f14691..6bc600d 100644
--- a/vmbase/src/memory/mod.rs
+++ b/vmbase/src/memory/mod.rs
@@ -25,5 +25,5 @@
 pub use shared::{alloc_shared, dealloc_shared, MemoryRange, MemoryTracker, MEMORY};
 pub use util::{
     flush, flushed_zeroize, min_dcache_line_size, page_4kb_of, phys_to_virt, virt_to_phys,
-    PAGE_SIZE, SIZE_2MB, SIZE_4KB, SIZE_4MB,
+    PAGE_SIZE, SIZE_128KB, SIZE_2MB, SIZE_4KB, SIZE_4MB,
 };