tower test: switch to use real TIM1_UP signal
tower testing helper: fix start memory address in linker script. test1 works!!

- test1_period should work right out of the box
- hacked together tick1_sig test works when you insert timer driver
  dependency, init, and clear calls yourself. (its a one-shot interrupt
  that goes off some fixed period after init - i'll make a more sophisticated
  example later)