MAINTAINERS: Add arm-soc tree entry

Document the arm-soc tree in the maintainers file so that
developers know how arm SoC development is structured.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

MAINTAINERS

@@ -637,6 +637,13 @@ W:	http://www.arm.linux.org.uk/
 S:	Maintained
 F:	arch/arm/
 
+ARM SUB-ARCHITECTURES
+L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
+S:	MAINTAINED
+F:	arch/arm/mach-*/
+F:	arch/arm/plat-*/
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc.git
+
 ARM PRIMECELL AACI PL041 DRIVER
 M:	Russell King <linux@arm.linux.org.uk>
 S:	Maintained