Update MIPS machine documentation to add Loongson-3 based machine description.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
---
 docs/system/target-mips.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/docs/system/target-mips.rst b/docs/system/target-mips.rst
index cd2a931..138441b 100644
--- a/docs/system/target-mips.rst
+++ b/docs/system/target-mips.rst
@@ -84,6 +84,16 @@ The Fuloong 2E emulation supports:
 
 -  RTL8139D as a network card chipset
 
+The Loongson-3 virtual platform emulation supports:
+
+-  Loongson 3A CPU
+
+-  LIOINTC as interrupt controller
+
+-  GPEX and virtio as peripheral devices
+
+-  Both KVM and TCG supported
+
 The mipssim pseudo board emulation provides an environment similar to
 what the proprietary MIPS emulator uses for running Linux. It supports:
 
-- 
2.7.0