sys/vfs/hammer: Define and use HAMMER_ENCODE() on blockmap formatting

- Add HAMMER_ENCODE() which is a generic version of existing
  macros HAMMER_ENCODE_{RAW_VOLUME|RAW_BUFFER|FREEMAP}().

- Use HAMMER_ENCODE() in format_blockmap() in userspace when newfs
  initializes blockmap offsets. This is better in the sense that
  the macro hides internal of hammer's storage address space format,
  and gets rid of bitwise operations that make assumption on format.

sbin/hammer/ondisk.c

@@ -817,8 +817,7 @@ void
 format_blockmap(hammer_blockmap_t blockmap, hammer_off_t zone_base)
 {
 	blockmap->phys_offset = 0;
-	blockmap->alloc_offset = zone_base | HAMMER_VOL_ENCODE(255) |
-				 HAMMER_SHORT_OFF_ENCODE(-1);
+	blockmap->alloc_offset = HAMMER_ENCODE(zone_base, 255, -1);
 	blockmap->first_offset = zone_base;
 	blockmap->next_offset = zone_base;
 	blockmap->entry_crc = crc32(blockmap, HAMMER_BLOCKMAP_CRCSIZE);

sys/vfs/hammer/hammer_disk.h

@@ -189,6 +189,11 @@ typedef u_int32_t hammer_crc_t;
 #define HAMMER_LONG_OFF_ENCODE(offset)			\
 	((hammer_off_t)(offset) & HAMMER_OFF_LONG_MASK)
 
+#define HAMMER_ENCODE(zone_base, vol_no, offset)	\
+	((zone_base) |					\
+	HAMMER_VOL_ENCODE(vol_no) |			\
+	HAMMER_SHORT_OFF_ENCODE(offset))
+
 #define HAMMER_ENCODE_RAW_VOLUME(vol_no, offset)	\
 	(HAMMER_ZONE_RAW_VOLUME |			\
 	HAMMER_VOL_ENCODE(vol_no) |			\