Docs: Fix Armclang toolchain descriptions

- Fix Armclang PATH setting
- Specify valid Armclang versions. It is found Armclang v6.15 and v6.16
  may also cause MemManage Fault as v6.17 does.

Change-Id: Id5a591a8d165c78adf5fd9346c962662f151d496
Signed-off-by: David Hu <david.hu@arm.com>
1 file changed