Improvement on backup-switchover-mode overlay value definitions (#5884)
For the RV3028 RTC, the definitions for its `backup-switchover-mode` overlay
were not intelligible neither complete/exhaustive.
Accordingly to the https://github.com/raspberrypi/linux/issues/2912#issuecomment-
477670051
these one here proposed should be correct.
`/boot/config.txt` should be as a configuration example, for rv3028, on a
Uputronics GPS Extension HAT:
# For GPS Expansion Board from Uputronics
dtparam=i2c_arm=on
dtoverlay=i2c-rtc,rv3028,backup-switchover-mode=3
dtoverlay=pps-gpio,gpiopin=18
init_uart_baud=115200
From my tests (`sudo rmmod rtc_rv3028 && sudo i2cget -y 1 0x52 0x37`):
`Default from factory`: `0x10`
`Mode 0`: `0x10`
`Mode 1`: `0x14`
`Mode 2`: `0x18`
`Mode 3`: `0x1c`
`Mode 3`: `0x1c` is consistent with the manufacturer configuration script: http://store.uputronics.com/files/configure-rv3028.sh