altos: Support ao_ms5607_dump when no ms5607 task

MicroPeak v2.0 has tasking support, but doesn't have a separate ms5607
task. That means the device isn't getting initialized when not running
the flight code, so in cmd mode we need to make sure it's initialized,
and we also need to actually fetch a value to display.

Signed-off-by: Keith Packard <keithp@keithp.com>