bnx2fc: Show information about log levels in 'modinfo'

This patch adds the information of the different values that can be used
in the module parameter 'debug_logging', as it is shown below:

$ modinfo bnx2fc
[...]
parm:           debug_logging:Option to enable extended logging,
		Default is 0 - no logging.
		0x01 - SCSI cmd error, cleanup.
		0x02 - Session setup, cleanup, etc.
		0x04 - lport events, link, mtu, etc.
		0x08 - ELS logs.
		0x10 - fcoe L2 fame related logs.
		0xff - LOG all messages. (int)

Signed-off-by: Jose Castillo <jcastillo@redhat.com>
Acked-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>