Add an "i2c-mux-base-bus-num" device property to i2c-mux-reg so
DT/ACPI/swnode instances can request a fixed base bus number; the
legacy platdata path already supports this via data.base_nr.

Patch 1 converts the legacy Documentation/devicetree/bindings/i2c/
i2c-mux-reg.txt binding to the YAML schema and documents the new
property. Patch 2 reads the property in the driver.

The series applies on top of the device-property accessor conversion
queued in Wolfram's wsa.git i2c/for-andi:

  c191ec71250b ("i2c: mux: reg: use device property accessors")
  https://lore.kernel.org/all/20260519-i2c-mux-reg-v6-1-a27ff50dee67@nexthop.ai/

Without that conversion there is no probe-time hook on the OF path
for the new property the driver reads.

Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
Abdurrahman Hussain (2):
      dt-bindings: i2c: convert i2c-mux-reg to DT schema
      i2c: mux: reg: allow fixing the base bus number via fwnode

 .../devicetree/bindings/i2c/i2c-mux-reg.txt        |  74 --------------
 .../devicetree/bindings/i2c/i2c-mux-reg.yaml       | 110 +++++++++++++++++++++
 drivers/i2c/muxes/i2c-mux-reg.c                    |   4 +-
 3 files changed, 113 insertions(+), 75 deletions(-)
---
base-commit: aa61612ab641d7d62b0b6889f2c7c9251489f6e3
change-id: 20260607-i2c-mux-reg-base-bus-num-738e5db7e99c
prerequisite-patch-id: 3ad9f5acb365e6eb2cd3b0790e983b9049371155

Best regards,
--  
Abdurrahman Hussain <abdurrahman@nexthop.ai>