Remove address space usage from Pagemap.

The pagemap allocates it self directly either from

  * the original fixed address range it is supplied, and returns the
    remaining space after the pagemap is removed; or
  * directly allocated from the PAL without using the address space
    manager.

This change in layering is required for the next commit, which imposes
the invariant that the pagemap has been committed for all spaced managed
by the address space manager.

src/test/func/pagemap/pagemap.cc

@@ -76,11 +76,22 @@ void test_pagemap(bool bounded)
   // Initialise the pagemap
   if (bounded)
   {
-    pagemap_test_bound.init(&address_space, low, high);
+    auto size = bits::one_at_bit(30);
+    auto base = address_space.reserve<true>(size);
+    std::cout << "Fixed base: " << base.unsafe_ptr() << " (" << size << ") "
+              << " end: " << pointer_offset(base, size).unsafe_ptr()
+              << std::endl;
+    auto [heap_base, heap_size] = pagemap_test_bound.init(base, size);
+    std::cout << "Heap base:  " << heap_base.unsafe_ptr() << " (" << heap_size
+              << ") "
+              << " end: " << pointer_offset(heap_base, heap_size).unsafe_ptr()
+              << std::endl;
+    low = address_cast(heap_base);
+    high = low + heap_size;
   }
   else
   {
-    pagemap_test_unbound.init(&address_space);
+    pagemap_test_unbound.init();
   }
 
   // Nullptr should still work after init.
@@ -95,7 +106,7 @@ void test_pagemap(bool bounded)
     value.v++;
     if (value.v == T().v)
       value = 0;
-    if ((ptr % (1ULL << 26)) == 0)
+    if (((ptr - low) % (1ULL << 26)) == 0)
       std::cout << "." << std::flush;
   }
 
@@ -110,7 +121,7 @@ void test_pagemap(bool bounded)
     if (value.v == T().v)
       value = 0;
 
-    if ((ptr % (1ULL << 26)) == 0)
+    if (((ptr - low) % (1ULL << 26)) == 0)
       std::cout << "." << std::flush;
   }
   std::cout << std::endl;