altos: Add pad support for new telefire versions

Makes the voltage divider values configurable, and allows for pyro
channels that don't have the resistors necessary to check for a stuck
relay.

Also supports STM32L processors with wider GPIO registers, and uses
the new ao_gpio_set/clr_bits functions to fire igniters rather than
cc1111-specific code.

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