powerpc/pmap: Enable UMA_MD_SMALL_ALLOC for 64-bit booke

The only thing blocking UMA_MD_SMALL_ALLOC from working on 64-bit booke
powerpc was a missing check in pmap_kextract().  Adding DMAP handling into
pmap_kextract(), we can now use UMA_MD_SMALL_ALLOC.  This should improve
performance and stability a bit, since DMAP is always mapped in TLB1, so
this relieves pressure on TLB0.

MFC after:	3 weeks

sys/powerpc/booke/pmap.c

@@ -1958,6 +1958,11 @@ mmu_booke_kextract(mmu_t mmu, vm_offset_t va)
 	vm_paddr_t p = 0;
 	int i;
 
+#ifdef __powerpc64__
+	if (va >= DMAP_BASE_ADDRESS && va <= DMAP_MAX_ADDRESS)
+		return (DMAP_TO_PHYS(va));
+#endif
+
 	if (va >= VM_MIN_KERNEL_ADDRESS && va <= VM_MAX_KERNEL_ADDRESS)
 		p = pte_vatopa(mmu, kernel_pmap, va);
 	

sys/powerpc/include/vmparam.h

@@ -133,6 +133,11 @@
 
 #else /* Book-E */
 
+/* Use the direct map for UMA small allocs on powerpc64. */
+#ifdef __powerpc64__
+#define UMA_MD_SMALL_ALLOC
+#endif
+
 #define	KERNBASE		0x04000100	/* start of kernel physical */
 #ifndef __powerpc64__
 #define	VM_MIN_KERNEL_ADDRESS	0xc0000000