Add a new 'tr' (transfer) mode to i2c(8) to support more i2c controllers.

Some i2c controller hardware does not provide a way to do individual START,
REPEAT-START and STOP actions on the i2c bus. Instead, they can only do
a complete transfer as a single operation. Typically they can do either
START-data-STOP or START-data-REPEATSTART-data-STOP. In the i2c driver
framework, this corresponds to the iicbus_transfer method. In the userland
interface they are initiated with the I2CRDWR ioctl command.

These changes add a new 'tr' mode which can be specified with the '-m'
command line option. This mode should work on all hardware; when an i2c
controller driver doesn't directly support the iicbus_transfer method,
code in the i2c driver framework uses the lower-level START/REPEAT/STOP
methods to implement the transfer. After this new mode has gotten some
testing on various hardware, the 'tr' mode should probably become the
new default mode.

PR: 189914