drivers: i2c: cc13xx_cc26xx: Add support for I2C_MSG_RESTART

Add support for the I2C_MSG_RESTART flag to be able to use a
repeated start in between chained transactions.
The driver now uses the stop/restart flags set in the i2c_msg,
instead of starting and stopping for each transaction in the chain.

Signed-off-by: Lorenz Clijnen <github@lorc.be>