powerpc: Fix DEBUG_HIGHMEM build break from d4515646

Code was added to mm/higmem.c that depends on several
kmap types that powerpc does not support.  We add dummy
invalid definitions for KM_NMI, KM_NM_PTE, and KM_IRQ_PTE.

According to list discussion, this fix should not be needed
anymore starting with 2.6.33.  The code is commented to this
effect so hopefully we will remember to remove this.
Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/kmap_types.h

@@ -29,5 +29,16 @@ enum km_type {
 	KM_TYPE_NR
 };
 
+/*
+ * This is a temporary build fix that (so they say on lkml....) should no longer
+ * be required after 2.6.33, because of changes planned to the kmap code.
+ * Let's try to remove this cruft then.
+ */
+#ifdef CONFIG_DEBUG_HIGHMEM
+#define KM_NMI		(-1)
+#define KM_NMI_PTE	(-1)
+#define KM_IRQ_PTE	(-1)
+#endif
+
 #endif	/* __KERNEL__ */
 #endif	/* _ASM_POWERPC_KMAP_TYPES_H */