`CC2650_FAST_RADIO_STARTUP` is required for TSCH, but it currently breaks ContikiMAC. We set the default value to the one that will work with the default choice of RDC.
Fixes#1744
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