docs: gxbb: Add documentation

Change-Id: Ie2465c1ccc482bd8eb5e5a71c580543095e4ba94
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

docs/plat/meson-gxbb.rst

+Trusted Firmware-A for Amlogic Meson S905 (GXBB)
+================================================
+
+The Amlogic Meson S905 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=gxbb bl31
+
+This port has been tested in a ODROID-C2. After building it, follow the
+instructions in the `U-Boot repository`_, replacing the mentioned **bl31.bin**
+by the one built from this port.
+
+.. _U-Boot repository: https://github.com/u-boot/u-boot/blob/master/board/amlogic/odroid-c2/README

maintainers.rst

@@ -26,6 +26,14 @@ Allwinner ARMv8 platform port
 :F: plat/allwinner/
 :F: drivers/allwinner/
 
+Amlogic Meson S905 (GXBB) platform port
+---------------------------------------
+:M: Antonio Niño Díaz <antonio.ninodiaz@arm.com>
+:G: `antonio-nino-diaz-arm`_
+:F: docs/plat/meson-gxbb.rst
+:F: drivers/meson/
+:F: plat/meson/gxbb/
+
 Armv7-A architecture port
 -------------------------
 :M: Etienne Carriere <etienne.carriere@linaro.org>

readme.rst

@@ -193,6 +193,7 @@ All the above platforms have been tested with `Linaro Release 18.04`_.
 This release also contains the following platform support:
 
 -  Allwinner sun50i_64 and sun50i_h6
+-  Amlogic Meson S905 (GXBB)
 -  ARM SGI-575 and SGM-775
 -  HiKey, HiKey960 and Poplar boards
 -  Marvell Armada 8K