Documentation: ABI: Add sysfs-class-reboot-mode-reboot_modes

Documentation: ABI: Add sysfs-class-reboot-mode-reboot_modes

Add ABI documentation for /sys/class/reboot-mode/*/reboot_modes, a
read-only sysfs attribute exposing the list of supported reboot-mode
arguments. This file is created by reboot-mode framework and provides a
user-readable interface to query available reboot-mode arguments.

Reviewed-by: Bartosz Golaszewski <brgl@kernel.org>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
Link: https://patch.msgid.link/20260224-next-15nov_expose_sysfs-v24-1-4ee5b49d5a06@oss.qualcomm.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>