devlink: Add devlink health diagnose command

devlink: Add devlink health diagnose command

Add devlink health diagnose command: enabling retrieval of diagnostics data
by the user on a reporter on a device. The command's output is a
free text defined by the reporter.

This patch also introduces an infra structure for flexible format
output. This allow the command to display different data fields
according to the reporter.
Example:
$ devlink health diagnose pci/0000:00:0a.0 reporter tx
SQs:
  sqn: 4403 HW state: 1 stopped: false
  sqn: 4408 HW state: 1 stopped: false
  sqn: 4413 HW state: 1 stopped: false
  sqn: 4418 HW state: 1 stopped: false
  sqn: 4423 HW state: 1 stopped: false

$ devlink health diagnose pci/0000:00:0a.0 reporter tx -jp
{
 "SQs":[
      {
       "sqn":4403,
       "HW state":1,
       "stopped":false
     },
      {
       "sqn":4408,
       "HW state":1,
       "stopped":false
     },
      {
       "sqn":4413,
       "HW state":1,
       "stopped":false
     },
      {
       "sqn":4418,
       "HW state":1,
       "stopped":false
     },
      {
       "sqn":4423,
       "HW state":1,
       "stopped":false
     }
   ]
}

Signed-off-by: Aya Levin <ayal@mellanox.com>
Reviewed-by: Moshe Shemesh <moshe@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David Ahern <dsahern@gmail.com>