kernel: Move aligned_alloc to heap.cpp alongside calloc.

It is independent of whatever heap implementation is actually in use,
so it belongs in here (even if this file is probably not the right
place for such functions in the first place.)

This allows the kernel to be built once again with things other than
the default slab heap.

src/system/kernel/heap.cpp

@@ -2493,6 +2493,16 @@ calloc(size_t numElements, size_t size)
 }
 
 
+void *
+aligned_alloc(size_t alignment, size_t size)
+{
+	if ((size % alignment) != 0)
+		return NULL;
+
+	return memalign(alignment, size);
+}
+
+
 void
 deferred_free(void *block)
 {

src/system/kernel/slab/allocator.cpp

@@ -229,16 +229,6 @@ posix_memalign(void** _pointer, size_t alignment, size_t size)
 }
 
 
-void *
-aligned_alloc(size_t alignment, size_t size)
-{
-	if ((size % alignment) != 0)
-		return NULL;
-
-	return memalign(alignment, size);
-}
-
-
 void
 free_etc(void *address, uint32 flags)
 {