doc: boards: amlogic: add documentation for BananaPi CM4IO

Add build instructions for the BananaPi BPI-CM4IO carrier board with
BPI-CM4 module.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Link: https://lore.kernel.org/r/20230320114609.930145-31-christianshewitt@gmail.com
[narmstrong: fixed doc build]
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
4 files changed