boards: amlogic: Fix boards README

Fix typos and update the supported devices for all Amlogic boards.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/arch/arm/mach-meson/Kconfig b/arch/arm/mach-meson/Kconfig
index cc3383a..7662256 100644
--- a/arch/arm/mach-meson/Kconfig
+++ b/arch/arm/mach-meson/Kconfig
@@ -17,7 +17,7 @@
 	select DM
 	select DM_SERIAL
 	help
-	  The Amlogic Meson GXL (S905X and S905X) is an ARM SoC with a
+	  The Amlogic Meson GXL (S905X and S905D) is an ARM SoC with a
 	  quad-core Cortex-A53 CPU and a Mali-450 GPU.
 
 if MESON_GXBB