docs: Add skeletal documentation of the emcraft-sf2

Add skeletal documentation of the emcraft-sf2 machine.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210713142226.19155-3-peter.maydell@linaro.org

MAINTAINERS

@@ -1024,6 +1024,7 @@ M: Peter Maydell <peter.maydell@linaro.org>
 L: qemu-arm@nongnu.org
 S: Maintained
 F: hw/arm/msf2-som.c
+F: docs/system/arm/emcraft-sf2.rst
 
 ASPEED BMCs
 M: Cédric Le Goater <clg@kaod.org>

docs/system/arm/emcraft-sf2.rst

@@ -0,0 +1,15 @@
+Emcraft SmartFusion2 SOM kit (``emcraft-sf2``)
+==============================================
+
+The ``emcraft-sf2`` board emulates the SmartFusion2 SOM kit from
+Emcraft (M2S010). This is a System-on-Module from EmCraft systems,
+based on the SmartFusion2 SoC FPGA from Microsemi Corporation.
+The SoC is based on a Cortex-M4 processor.
+
+Emulated devices:
+
+- System timer
+- System registers
+- SPI controller
+- UART
+- EMAC

docs/system/target-arm.rst

@@ -86,6 +86,7 @@ undocumented; you can get a complete list by running
    arm/sabrelite
    arm/digic
    arm/cubieboard
+   arm/emcraft-sf2
    arm/musicpal
    arm/gumstix
    arm/nrf