maintainers: Update maintainer for sgi/sgm platforms

maintainers.rst

@@ -30,6 +30,15 @@ Armv7-A architecture port
 :M: Etienne Carriere <etienne.carriere@linaro.org>
 :G: `etienne-lms`_
 
+Arm System Guidance for Infrastructure / Mobile FVP platforms
+-------------------------------------------------------------
+:M: Nariman Poushin <nariman.poushin@linaro.org>
+:G: `nariman`_
+:F: plat/arm/css/sgi/
+:F: plat/arm/css/sgm/
+:F: plat/arm/board/sgi575/
+:F: plat/arm/board/sgm775/
+
 eMMC/UFS drivers
 ----------------
 :M: Haojian Zhuang <haojian.zhuang@linaro.org>
@@ -186,6 +195,7 @@ Xilinx platform port
 .. _kostapr: https://github.com/kostapr
 .. _masahir0y: https://github.com/masahir0y
 .. _mtk09422: https://github.com/mtk09422
+.. _nariman: https://github.com/npoushin
 .. _qoriq-open-source: https://github.com/qoriq-open-source
 .. _rockchip-linux: https://github.com/rockchip-linux
 .. _shawnguo2: https://github.com/shawnguo2