[media] v4l2-ctrls: eliminate lockdep false alarms for struct v4l2_ctrl_handler.lock

[media] v4l2-ctrls: eliminate lockdep false alarms for struct v4l2_ctrl_handler.lock

When calling v4l2_ctrl_add_handler(), lockdep would detect a potential
recursive locking problem on a situation that is by design intended and
not a recursive lock.  This happened because all struct
v4l2_ctrl_handler.lock mutexes were created as members of the same lock
class in v4l2_ctrl_handler_init(), and v4l2_ctrl_add_handler() takes the
hdl->lock on two different v4l2_ctrl_handler instances.
This change breaks the large lockdep lock class for struct
v4l2_ctrl_handler.lock and breaks it into v4l2_ctrl_handler
instantiation specific lock classes with meaningful class names.
This will validly eliminate lockdep alarms for v4l2_ctrl_handler locking
validation, as long as the relationships between drivers adding v4l2
controls to their own handler from other v4l2 drivers' control handlers
remains straightforward.
struct v4l2_ctrl_handler.lock lock classes are created with names such
that the output of cat /proc/lockdep indicates where in the v4l2 driver
code v4l2_ctrl_handle_init() is being called on instantiations:
ffffffffa045f490 FD:   10 BD:    8 +.+...: cx2341x:1534:(hdl)->lock
ffffffffa0497d20 FD:   12 BD:    2 +.+.+.: saa7115:1581:(hdl)->lock
ffffffffa04ac660 FD:   14 BD:    2 +.+.+.: msp3400_driver:756:(hdl)->lock
ffffffffa0484b90 FD:   12 BD:    1 +.+.+.: ivtv_gpio:366:(&itv->hdl_gpio)->lock
ffffffffa04eb530 FD:   11 BD:    2 +.+.+.: cx25840_core:1982:(&state->hdl)->lock
ffffffffa04fbc80 FD:   11 BD:    3 +.+.+.: wm8775:246:(&state->hdl)->lock
Some lock chains, that were previously causing the recursion alarms, are
now visible in the output of cat /proc/lockdep_chains:
irq_context: 0
[ffffffffa0497d20] saa7115:1581:(hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa04ac660] msp3400_driver:756:(hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa0484b90] ivtv_gpio:366:(&itv->hdl_gpio)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa04eb530] cx25840_core:1982:(&state->hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock
irq_context: 0
[ffffffffa04fbc80] wm8775:246:(&state->hdl)->lock
[ffffffffa045f490] cx2341x:1534:(hdl)->lock

Signed-off-by: Andy Walls <awalls@md.metrocast.net>
[hans.verkuil@cisco.com: keep mutex_init in v4l2_ctrl_handler_init_class]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>