Documentation: power: rt9471: Document exported sysfs entries

Document the settings exported by rt9471 charger driver through sysfs entries:
- sysoff_enable
- port_detect_enable

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
[update kernel version and date]
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

diff --git a/Documentation/ABI/testing/sysfs-class-power-rt9471 b/Documentation/ABI/testing/sysfs-class-power-rt9471
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+What:          /sys/class/power_supply/rt9471-*/sysoff_enable
+Date:          Feb 2023
+KernelVersion: 6.3
+Contact:       ChiYuan Huang <cy_huang@richtek.com>
+Description:
+               This entry allows enabling the sysoff mode of rt9471 charger devices.
+               If enabled and the input is removed, the internal battery FET is turned
+               off to reduce the leakage from the BAT pin. See device datasheet for details.
+               It's commonly used when the product enter shipping stage. After entering
+               shipping mode, only 'VBUS' or 'Power key" pressed can make it leave this
+               mode. 'Disable' also can help to leave it, but it's more like to abort
+               the action before the device really enter shipping mode.
+
+               Access: Read, Write
+               Valid values:
+               - 1: enabled
+               - 0: disabled
+
+What:          /sys/class/power_supply/rt9471-*/port_detect_enable
+Date:          Feb 2023
+KernelVersion: 6.3
+Contact:       ChiYuan Huang <cy_huang@richtek.com>
+Description:
+               This entry allows enabling the USB BC12 port detect function of rt9471 charger
+               devices. If enabled and VBUS is inserted, device will start to do the BC12
+               port detect and report the usb port type when port detect is done. See
+               datasheet for details. Normally controlled when TypeC/USBPD port integrated.
+
+               Access: Read, Write
+               Valid values:
+               - 1: enabled
+               - 0: disabled