* Improved SDRAM refresh timings for Pi5 - 16GB
* Add an option to wait for the power button to be pressed before booting.
If POWER_OFF_ON_HALT=1 and WAIT_FOR_POWER_BTN=1 in the bootloader
config then the bootloader will wait for either the power button
to be pressed or an RTC alarm before booting. The wait state
switches the PMIC to STANDBY mode which is the lowest possible
power state.
