[umalloc] Split largest_memblock() function out from init_eheap()

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/memblock.h

@@ -0,0 +1,17 @@
+#ifndef _IPXE_MEMBLOCK_H
+#define _IPXE_MEMBLOCK_H
+
+/** @file
+ *
+ * Largest memory block
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <ipxe/uaccess.h>
+
+extern size_t largest_memblock ( userptr_t *start );
+
+#endif /* _IPXE_MEMBLOCK_H */