MAINTAINERS: Add ti-sysc files under the OMAP2+ entry

Add the ti-sysc source files under the OMAP2+ entry so that
the get_maintainer script also generates the linux-omap
list to be cc'd for all patches touching these files.

Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>