sgi/distro: allow this script to be usable on SGI-Clark.Helios platform

SGI-Clark.Helios platform supports booting most of common distributions.
So allow this script to be usable on SGI-Clark.Helios platform.

Change-Id: I3d52a6fc9700079d040b97aec7e47f055eaed339
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>

sgi/distro.sh

@@ -39,6 +39,7 @@ extra_param=""
 declare -A sgi_platforms
 sgi_platforms[sgi575]=1
 sgi_platforms[sgiclarka]=1
+sgi_platforms[sgiclarkh]=1
 
 __print_supported_sgi_platforms()
 {