Define VM_KMEM_SIZE_MAX on sparc64. Otherwise kernel built with

DEBUG_MEMGUARD panics early in kmeminit() with the message
"kmem_suballoc: bad status return of 1" because of zero "size" argument
passed to kmem_suballoc() due to "vm_kmem_size_max" being zero.

The problem also exists on ia64.

sys/sparc64/include/vmparam.h

@@ -236,6 +236,14 @@
 #define	VM_KMEM_SIZE_SCALE	(3)
 #endif
 
+/*
+ * Ceiling on amount of kmem_map kva space.
+ */
+#ifndef VM_KMEM_SIZE_MAX
+#define	VM_KMEM_SIZE_MAX	((VM_MAX_KERNEL_ADDRESS - \
+    VM_MIN_KERNEL_ADDRESS + 1) * 3 / 5)
+#endif
+
 /*
  * Initial pagein size of beginning of executable file.
  */