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:
* Moves all cpu files from cpu/cc26xx to cpu/cc26xx-cc13xx
* Bumps the CC26xxware submodule to the latest TI release
* Adds CC13xxware as a submodule
* Adds support for sub-ghz mode / IEEE 802.15.4g
* Splits the driver into multiple files for clarity. We now have the following structure:
* A common module that handles access to the RF core, interrupts etc
* A module that takes care of BLE functionality
* A netstack radio driver for IEEE mode (2.4GHz)
* A netstack radio driver for PROP mode (sub-ghz - multiple bands)
This commit also adds tick suppression functionality, applicable to all chips of the CC26xx and CC13xx families. Instead waking up on every clock tick simply to increment our software counter, we now only wake up just in time to service the next scheduled etimer. ContikiMAC-triggered wakeups are unaffected.
Laslty, this commit also applies a number of minor changes:
* Addition of missing includes
* Removal of stub functions
* Removal of a woraround for a CC26xxware bug that has now been fixed
