This commit updates the srf06-cc26xx platform by adding support for the CC1310EM.
We generalise the way this platform selects CPU/board so that we can easily add more combinations in the future. These changes have implication on how to build for different devices, so make sure to have a look at the updated README
We only power, clock and enable the peripepheral when / if we need it
* We no longer automatically turn on the SERIAL PD when the CM3 is running
* Make sure the I2C peripheral is accessible (powered and clocked) before any operation
* If the peripheral is not accessible, automatically power it up and run the clock
* Put SDA, SCL, SDA HP and SCL HP in a low-leakage state when shutting down
* Don't automatically fire up the I2C controller when we wake up
