altos: Fixed timing of panic display LED to be readable

altos: Fixed timing of panic display LED to be readable

When we don't have a beeper, there's no way to signal a 'warble' for
panic. So, elide that bit.

Second, panic can't use the scheduler and timer because those may not
be running (or may have failed), and so it uses a delay loop. Add a
configurable scale value to the panic loop so that the LED blinks can
be read. For stm32f0 devices, scale that by the sysclk value to
automatically make them of reasonable length.