i2c: Allow dumping the data of read messages

Add an argument to i2c_dump_msgs() to log the data from reads too.  And
then rename the function to i2c_dump_msgs_rw() so the API doesn't
change.  If the dump is done after a transaction is processed, as
opposed to before, then the read data is valid and can be very useful.

Signed-off-by: Trent Piepho <trent.piepho@igorinstitute.com>