feat(stm32mp21): add PWR registers file

Use the new file stm32mp21_pwr.h for STM32MP21 PWR peripheral registers
definition. Update platform code for backup domain write protection
disabling.

Change-Id: Iedfa764529bcd5119be8e94da7f7b84699e86086
Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
3 files changed