ide: replace the global ide_lock spinlock by per-hwgroup spinlocks (v2)

Now that (almost) all host drivers have been fixed not to abuse ide_lock
and core code usage of ide_lock has been sanitized we may safely replace
ide_lock by per-hwgroup locks.

This patch is partially based on earlier patch from Ravikiran G Thirumalai.

While at it:
- don't use deprecated HWIF() and HWGROUP() macros
- update locking documentation in ide.h

v2:
Add missing spin_lock_init(&hwgroup->lock).  (Noticed by Elias Oltmanns)

Cc: Vaibhav V. Nivargi <vaibhav.nivargi@gmail.com>
Cc: Alok N. Kataria <alokk@calsoftinc.com>
Cc: Shai Fultheim <shai@scalex86.org>
Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Cc: Elias Oltmanns <eo@nebensachen.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

include/linux/ide.h

@@ -909,6 +909,8 @@ typedef struct hwgroup_s {
 
 	int req_gen;
 	int req_gen_timer;
+
+	spinlock_t lock;
 } ide_hwgroup_t;
 
 typedef struct ide_driver_s ide_driver_t;
@@ -1610,13 +1612,13 @@ extern struct mutex ide_cfg_mtx;
 /*
  * Structure locking:
  *
- * ide_cfg_mtx and ide_lock together protect changes to
- * ide_hwif_t->{next,hwgroup}
+ * ide_cfg_mtx and hwgroup->lock together protect changes to
+ * ide_hwif_t->next
  * ide_drive_t->next
  *
- * ide_hwgroup_t->busy: ide_lock
- * ide_hwgroup_t->hwif: ide_lock
- * ide_hwif_t->mate: constant, no locking
+ * ide_hwgroup_t->busy: hwgroup->lock
+ * ide_hwgroup_t->hwif: hwgroup->lock
+ * ide_hwif_t->{hwgroup,mate}: constant, no locking
  * ide_drive_t->hwif: constant, no locking
  */