docs: Add documentation of Arm 'mainstone' board

Add brief documentation of the Arm 'mainstone' board.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210722175229.29065-2-peter.maydell@linaro.org

MAINTAINERS

@@ -856,6 +856,7 @@ F: include/hw/arm/pxa.h
 F: include/hw/arm/sharpsl.h
 F: include/hw/display/tc6393xb.h
 F: docs/system/arm/xscale.rst
+F: docs/system/arm/mainstone.rst
 
 SABRELITE / i.MX6
 M: Peter Maydell <peter.maydell@linaro.org>

docs/system/arm/mainstone.rst

@@ -0,0 +1,25 @@
+Intel Mainstone II board (``mainstone``)
+========================================
+
+The ``mainstone`` board emulates the Intel Mainstone II development
+board, which uses a PXA270 CPU.
+
+Emulated devices:
+
+- Flash memory
+- Keypad
+- MMC controller
+- 91C111 ethernet
+- PIC
+- Timer
+- DMA
+- GPIO
+- FIR
+- Serial
+- LCD controller
+- SSP
+- USB controller
+- RTC
+- PCMCIA
+- I2C
+- I2S

docs/system/target-arm.rst

@@ -90,6 +90,7 @@ undocumented; you can get a complete list by running
    arm/highbank
    arm/musicpal
    arm/gumstix
+   arm/mainstone
    arm/nrf
    arm/nseries
    arm/nuvoton