test(realm): add new api to create and activate realm

* Add new API to create realm payload and activate realm.
  host_create_activate_realm_payload().
* Also add API to create realm without activate.
  host_create_realm_payload(). Host will need to call
  host_realm_activate() separately prior to entering.

Change-Id: I67c330c2672a02438cbb9a99c6c1741d3eda3cc3
Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
6 files changed