CC3200: Fix boot loader regression

Go back to Ubuntu 16.04 and older gcc-arm (4.9.3).

Boot loader just won't run when compiled with newer GCC (7.x).
It's likely that it can be fixed with compile switches but I couldn't figure it out quickly, so going to just downgrade for now to get it back to workign state.

CL: CC3200: Fix boot loader regression

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