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

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 <[email protected]>
Cc: Alok N. Kataria <[email protected]>
Cc: Shai Fultheim <[email protected]>
Signed-off-by: Ravikiran Thirumalai <[email protected]>
Cc: Elias Oltmanns <[email protected]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[email protected]>