The I2C master driver support for the RTL8721Dx (pke8721daf) and RTL8721F
(rtl8721f_evb) boards was merged without the matching board documentation.
Add the missing I2C entry to each board's Features list and an "i2c"
configuration section describing the /dev/i2cN devices, the board pin
table, and the i2ctool usage, mirroring the existing gpio/uart sections.
Signed-off-by: dechao_gong <dechao_gong@realsil.com.cn>
Assisted-by: Claude <noreply@anthropic.com>