The block that controls the `.upload` target is unnecessarily replicated in multiple sub-board Makefiles. This was originally done because the SmartRF and the Launchpad can be programmed with the c2538-bsl script, whereas the sensortag cannot.
This commit moves the `cc2538-bsl` / `.upload` target logic to the top level cpu Makefile (`cpu/cc26xx-cc13xx/Makefile.cc26xx-cc13xx`). Board makefiles simply set the make variable `BOARD_SUPPORTS_BSL` to 1 to signal that they can be programmed by the BSL script. If `BOARD_SUPPORTS_BSL` is not equal to 1, trying to use the `.upload` target will return an error message.
For example:
```
$ make BOARD=sensortag/cc2650 cc26xx-demo.upload
using saved target 'srf06-cc26xx'
This board cannot be programmed with the ROM bootloader and therefore does not support the .upload target.
```
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
Instead of using a separate data structure to request that a PD remain powered during deep sleep,
we do the same within the main LPM data structure through an additional field.
This allows us to maintain only one linked list of LPM modules and overall improves code clarity
