ide: make drive->id an union (take 2)

Make drive->id an unnamed union so id can be accessed either by using
'u16 *id' or 'struct hd_driveid *driveid'.  Then convert all existing
drive->id users accordingly (using 'u16 *id' when possible).

This is an intermediate step to make ide 'struct hd_driveid'-free.

While at it:

- Add missing KERN_CONTs in it821x.c.

- Use ATA_ID_WORDS and ATA_ID_*_LEN defines.

- Remove unnecessary checks for drive->id.

- s/drive_table/table/ in ide_in_drive_list().

- Cleanup ide_config_drive_speed() a bit.

- s/drive1/dev1/ & s/drive0/dev0/ in ide_undecoded_slave().

v2:
Fix typo in drivers/ide/ppc/pmac.c. (From Stephen Rothwell)

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/ppc/pmac.c b/drivers/ide/ppc/pmac.c
index fa2be26..c3432da 100644
--- a/drivers/ide/ppc/pmac.c
+++ b/drivers/ide/ppc/pmac.c
@@ -669,9 +669,9 @@
 set_timings_mdma(ide_drive_t *drive, int intf_type, u32 *timings, u32 *timings2,
 		 	u8 speed)
 {
+	u16 *id = drive->id;
 	int cycleTime, accessTime = 0, recTime = 0;
 	unsigned accessTicks, recTicks;
-	struct hd_driveid *id = drive->id;
 	struct mdma_timings_t* tm = NULL;
 	int i;
 
@@ -686,8 +686,8 @@
 	}
 
 	/* Check if drive provides explicit DMA cycle time */
-	if ((id->field_valid & 2) && id->eide_dma_time)
-		cycleTime = max_t(int, id->eide_dma_time, cycleTime);
+	if ((id[ATA_ID_FIELD_VALID] & 2) && id[ATA_ID_EIDE_DMA_TIME])
+		cycleTime = max_t(int, id[ATA_ID_EIDE_DMA_TIME], cycleTime);
 
 	/* OHare limits according to some old Apple sources */	
 	if ((intf_type == controller_ohare) && (cycleTime < 150))