Add support to run multiple action in single build command

earlier only one of clean/build/package could be provided with build
script, add support to run multiple build actions with single build
command e.g.

$ ./build-scripts/build-hafnium.sh -p aemfvp-a-rme clean build package

Signed-off-by: Jagdish Gediya <jagdish.gediya@arm.com>