tools: move tools targets to a separate makefile

The tools targets in the makefile at the base directory are moved
to another makefile under the tools directory. This provides a cleaner
separation for tools targets.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Tianyu Li <tianyu.li@arm.com>
Reviewed-by: Lijian Zhang <lijian.zhang@arm.com>
Reviewed-by: Nathan Brown <nathan.brown@arm.com>

Change-Id: I03704a8b5e029110f6936d3e878f1e09dd31914e