Added tracepoints in mailbox code so that
the mailbox operations like message allocation,
sending message and message interrupts are traced.
Also the mailbox errors occurred like timeout
or wrong responses are traced.
These will help in debugging mailbox issues.

Here's an example output showing one of the mailbox
messages sent by PF to AF and AF responding to it:

~# mount -t tracefs none /sys/kernel/tracing/
~# echo 1 > /sys/kernel/tracing/events/rvu/enable
~# ifconfig eth0 up
~# cat /sys/kernel/tracing/trace

~# cat /sys/kernel/tracing/trace
 tracer: nop

		      _-----=> irqs-off
		     / _----=> need-resched
		    | / _---=> hardirq/softirq
		    || / _--=> preempt-depth
		    ||| /     delay
   TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
      | |       |   ||||       |         |
ifconfig-2382  [002] ....   756.161892: otx2_msg_alloc: [0002:02:00.0] msg:(0x400) size:40

ifconfig-2382  [002] ...1   756.161895: otx2_msg_send: [0002:02:00.0] sent 1 msg(s) of size:48

 <idle>-0     [000] d.h1   756.161902: otx2_msg_interrupt: [0002:01:00.0] mbox interrupt PF(s) to AF (0x2)

kworker/u49:0-1165  [000] ....   756.162049: otx2_msg_process: [0002:01:00.0] msg:(0x400) error:0

kworker/u49:0-1165  [000] ...1   756.162051: otx2_msg_send: [0002:01:00.0] sent 1 msg(s) of size:32

kworker/u49:0-1165  [000] d.h.   756.162056: otx2_msg_interrupt: [0002:02:00.0] mbox interrupt AF to PF (0x1)
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>