Improvements in STM32 ADC
arch/arm/src/stm32/stm32_adc.c: start conversion on startup is now possible if TIM triggering selected. This can be useful to start ADC TIM conversion for ADC IPv2 when opening ADC device.
arch/arm/src/stm32/stm32_adc.c: fix compilation errors for chips with one ADV TIM
configs/nucleo-f303re: refresh ADC example
configs/nucleo-f334r8: refresh ADC example
Approved-by: GregoryN <gnutt@nuttx.org>