doc: boards: amlogic: add documentation for GS-King-X

GS-King-X is also supported with the beelink-s922x FIP sources and can use
the GT-King defconfig. Add a board document with instructions.

Signed-off-by: Christian Hewitt <christianshewitt@gmail.com>
Link: https://lore.kernel.org/r/20230320114609.930145-33-christianshewitt@gmail.com
[narmstrong: fixed doc build]
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
diff --git a/board/amlogic/beelink-s922x/MAINTAINERS b/board/amlogic/beelink-s922x/MAINTAINERS
index 47b6227..8dddeb9 100644
--- a/board/amlogic/beelink-s922x/MAINTAINERS
+++ b/board/amlogic/beelink-s922x/MAINTAINERS
@@ -3,8 +3,9 @@
 S:	Maintained
 L:	u-boot-amlogic@groups.io
 F:	board/amlogic/beelink-s922x/
+F:	configs/beelink-gsking-x_defconfig
 F:	configs/beelink-gtking_defconfig
 F:	configs/beelink-gtkingpro_defconfig
-F:	configs/beelink-gsking-x_defconfig
+F:	doc/board/amlogic/beelink-gskingx.rst
 F:	doc/board/amlogic/beelink-gtking.rst
 F:	doc/board/amlogic/beelink-gtkingpro.rst