spmi: add command tracepoints for SPMI

spmi: add command tracepoints for SPMI

Add tracepoints to retrieve information about read, write
and non-data commands. For performance measurement support
tracepoints are added at the beginning and at the end of
transfers. Following is a list showing the new tracepoint
events. The "cmd" parameter here represents the opcode, SID,
and full 16-bit address.

spmi_write_begin: cmd and data buffer.
spmi_write_end  : cmd and return value.
spmi_read_begin : cmd.
spmi_read_end   : cmd, return value and data buffer.
spmi_cmd        : cmd.

The reason that cmd appears at both the beginning and at
the end event is that SPMI drivers can request commands
concurrently. cmd helps in matching the corresponding
events.

SPMI tracepoints can be enabled like:

echo 1 >/sys/kernel/debug/tracing/events/spmi/enable

and will dump messages that can be viewed in
/sys/kernel/debug/tracing/trace that look like:

... spmi_read_begin: opc=56 sid=00 addr=0x0000
... spmi_read_end: opc=56 sid=00 addr=0x0000 ret=0 len=02 buf=0x[01-40]
... spmi_write_begin: opc=48 sid=00 addr=0x0000 len=3 buf=0x[ff-ff-ff]

Suggested-by: Sagar Dharia <sdharia@codeaurora.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>
Signed-off-by: Ankit Gupta <ankgupta@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>