arm: add support for Hisilicon HiSTB family SoCs

First supported chip is hi3798mv200 (which is similar to Hi3798cv200
used by poplar).

Signed-off-by: Yang Xiwen <forbidden405@outlook.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 706b831..703b1c2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -291,6 +291,7 @@
 F:	arch/arm/cpu/armv8/hisilicon
 F:	arch/arm/include/asm/arch-hi6220/
 F:	arch/arm/include/asm/arch-hi3660/
+F:	arch/arm/mach-histb
 
 ARM HPE GXP ARCHITECTURE
 M:	Jean-Marie Verdun <verdun@hpe.com>