update libopencm3

This brings in the new ADC api for STM32 parts.

Update to new standardized ADC apis.
Drops pointless channel definitions, uses common names for common functions.
No functional changes.

Based on work in: https://github.com/libopencm3/libopencm3-examples/pull/130

examples/stm32/f1/stm32vl-discovery/adc-dac-printf/adc-dac-printf.c

@@ -95,7 +95,7 @@ static void adc_setup(void)
 	gpio_set_mode(GPIOA, GPIO_MODE_INPUT, GPIO_CNF_INPUT_ANALOG, GPIO1);
 
 	/* Make sure the ADC doesn't run during config. */
-	adc_off(ADC1);
+	adc_power_off(ADC1);
 
 	/* We configure everything for one single conversion. */
 	adc_disable_scan_mode(ADC1);