Add support to disable cpu's in multicore processors

Add a disable sub-command to the cpu command that allows for disabling
cores in multicore processors.  This can be useful for systems that are
using multicore chips but aren't utilizing all the cores as a way to
reduce power and possibly improve performance.

Also updated an added missing copyright.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

include/common.h

@@ -712,6 +712,7 @@ void show_boot_progress(int val);
 #ifdef CONFIG_MP
 int cpu_status(int nr);
 int cpu_reset(int nr);
+int cpu_disable(int nr);
 int cpu_release(int nr, int argc, char *argv[]);
 #endif