plat: gxl: Add documentation on building GXL image

Also adds a maintainer for GXL.
Signed-off-by: Remi Pommarel <repk@triplefau.lt>

docs/plat/meson-gxl.rst

+Trusted Firmware-A for Amlogic Meson S905x (GXL)
+================================================
+
+The Amlogic Meson S905x is a SoC with a quad core Arm Cortex-A53 running at
+1.5Ghz. It also contains a Cortex-M3 used as SCP.
+
+This port is a minimal implementation of BL31 capable of booting mainline U-Boot
+and Linux:
+
+- SCPI support.
+- Basic PSCI support (CPU_ON, CPU_OFF, SYSTEM_RESET, SYSTEM_OFF). Note that CPU0
+  can't be turned off, so there is a workaround to hide this from the caller.
+- GICv2 driver set up.
+- Basic SIP services (read efuse data, enable/disable JTAG).
+
+In order to build it:
+
+::
+
+    CROSS_COMPILE=aarch64-linux-gnu- make DEBUG=1 PLAT=gxl
+
+This port has been tested on a Lepotato. After building it, follow the
+instructions in the `gxlimg repository` or `U-Boot repository`_, replacing the
+mentioned **bl31.img** by the one built from this port.
+
+.. _gxlimg repository: https://github.com/repk/gxlimg/blob/master/README
+.. _U-Boot repository: https://github.com/u-boot/u-boot/blob/master/board/amlogic/p212/README.libretech-cc

maintainers.rst

@@ -34,6 +34,14 @@ Amlogic Meson S905 (GXBB) platform port
 :F: drivers/meson/
 :F: plat/meson/gxbb/
 
+Amlogic Meson S905x (GXL) platform port
+---------------------------------------
+:M: Remi Pommarel <repk@triplefau.lt>
+:G: `remi-triplefault`_
+:F: docs/plat/meson-gxl.rst
+:F: drivers/meson/gxl
+:F: plat/meson/gxl/
+
 Armv7-A architecture port
 -------------------------
 :M: Etienne Carriere <etienne.carriere@linaro.org>
@@ -272,6 +280,7 @@ Xilinx platform port
 .. _mtk09422: https://github.com/mtk09422
 .. _npoushin: https://github.com/npoushin
 .. _qoriq-open-source: https://github.com/qoriq-open-source
+.. _remi-triplefault: https://github.com/repk
 .. _rockchip-linux: https://github.com/rockchip-linux
 .. _shawnguo2: https://github.com/shawnguo2
 .. _sivadur: https://github.com/sivadur

readme.rst

@@ -211,6 +211,7 @@ This release also contains the following platform support:
 
 -  Allwinner sun50i_a64 and sun50i_h6
 -  Amlogic Meson S905 (GXBB)
+-  Amlogic Meson S905x (GXL)
 -  Arm Juno Software Development Platform
 -  Arm Neoverse N1 System Development Platform (N1SDP)
 -  Arm Neoverse Reference Design N1 Edge (RD-N1-Edge) FVP