bus: ti-sysc: Switch to SPDX license identifier

Use the appropriate SPDX license identifier in the TI sysc
interconnect target driver source files and drop the previous
boilerplate license text. Also, add the the SPDX license
identifier in the associated ti-sysc header 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>