rtc: rv3028: Add support for setting the backup switching mode
By default the RV3028 does not switch to the backup voltage supply at all, if the main supply is shut down. Let's add the possibility to set the backup switching mode by programming the BSM bits in the backup register.
0x0: No switching 0x4: Direct Switching Mode (DSM) 0xc: Level Switching Mode (LSM)
Signed-off-by: Frieder Schrempf frieder.schrempf@kontron.de