Add basic support for the Epson RX8901CE RTC.
Datasheet: https://download.epsondevice.com/td/pdf/app/RX8901CE_en.pdf

Also includes a bug fix for an issue with reading the weekday from the
RTC which affects both the existing rx8130 and this rx8901 driver.

Signed-off-by: Fredrik M Olsson <fredrik.m.olsson@axis.com>
---
Changes in v2:
- Squashed the Voltage Low status patch into the driver patch
- Switch from dev_err to dev_dbg
- Implement Backup Switch Mode (BSM) ioctl instead of hard coding
  switching mode.
- Change the prototype for the do_trickle_setup function pointer in
  order to make it possible to propagate error codes from the added
  PWSW_CFG register read operation. This read operation is added so not
  to override previously set register fields.
- Link to v1: https://lore.kernel.org/r/20251219-ds1307-rx8901-add-v1-0-b13f346ebe93@axis.com

---
Fredrik M Olsson (3):
      dt-bindings: rtc: ds1307: Add epson,rx8901
      rtc: ds1307: Fix off-by-one issue with wday for rx8130
      rtc: ds1307: Add driver for Epson RX8901CE

 .../devicetree/bindings/rtc/rtc-ds1307.yaml        |   1 +
 drivers/rtc/rtc-ds1307.c                           | 218 ++++++++++++++++++++-
 2 files changed, 209 insertions(+), 10 deletions(-)
---
base-commit: 27fa82620cbaa89a7fc11ac3057701d598813e87
change-id: 20251126-ds1307-rx8901-add-a0fe173093e3

Best regards,
-- 
Fredrik M Olsson <fredrik.m.olsson@axis.com>