i2c: add tracepoints for I2C slave events

I2C slave events tracepoints can be enabled by:

	echo 1 > /sys/kernel/tracing/events/i2c_slave/enable

and logs in /sys/kernel/tracing/trace will look like:

	... i2c_slave: i2c-0 a=010 ret=0 WR_REQ []
	... i2c_slave: i2c-0 a=010 ret=0 WR_RCV [02]
	... i2c_slave: i2c-0 a=010 ret=0 WR_RCV [0c]
	... i2c_slave: i2c-0 a=010 ret=0   STOP []
	... i2c_slave: i2c-0 a=010 ret=0 RD_REQ [04]
	... i2c_slave: i2c-0 a=010 ret=0 RD_PRO [b4]
	... i2c_slave: i2c-0 a=010 ret=0  STOP []

formatted as:

	i2c-<adapter_nr>
	a=<addr>
	ret=<ret>	<- callback return value
	<event>
	[<data>]

trace printings can be selected by adding a filter like:

	echo adapter_nr==1 >/sys/kernel/tracing/events/i2c_slave/filter

Signed-off-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>