Allow the size argument for law_enable() to be non-power-of-2.

Although the local access windows are powers of 2 in size, allow arguments that
aren't power of 2, and round up.

sys/powerpc/mpc85xx/mpc85xx.c

@@ -157,7 +157,8 @@ law_find_free(void)
 	return (i);
 }
 
-#define	_LAW_SR(trgt,size)	(0x80000000 | (trgt << 20) | (ffsl(size) - 2))
+#define	_LAW_SR(trgt,size)	(0x80000000 | (trgt << 20) | \
+				(flsl(size + (size - 1)) - 2))
 
 int
 law_enable(int trgt, uint64_t bar, uint32_t size)