IVGCVSW-7201 Generalize get_compute_library.sh usage

* Allow user-specified directory name for the ACL
  repo (other than 'clframework') with the '-n'
  option.
* Fix indentation.

Signed-off-by: James Conroy <james.conroy@arm.com>
Change-Id: Iadec158bd9469fbc0d0875b085a5702e4a89ae83