drivers: counter: Do not keep RTC value between resets on STM32

This commit changes the ability to keep the RTC value between resets, and
turns it off by default.
Though this feature makes sense for an RTC counting the time and date,
here it is used as a counter. As such the registers used for coutning
should be reset after each MCU reset.

This change puts back in place the previous behavior before the Kconfig
CONFIG_COUNTER_RTC_STM32_BACKUP_DOMAIN_RESET was removed.

Signed-off-by: Guillaume Gautier <guillaume.gautier-ext@st.com>