arm-systemready: Add parted dependency and inherit testimage

Add the parted-native dependency explicitly which is needed to
use wic commands.

Also explicitly inherit testimage. This means that the kas config
is no longer required to include it in IMAGE_CLASSES.

Signed-off-by: Debbie Martin <Debbie.Martin@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>

kas/arm-systemready-ir-acs.yml

@@ -8,10 +8,5 @@ env:
   # The full testimage run typically takes around 12-24h on fvp-base.
   TEST_OVERALL_TIMEOUT: "${@ 24*60*60}"
 
-local_conf_header:
-  systemready-ir-acs: |
-    IMAGE_CLASSES:append = " testimage"
-
-
 target:
   - arm-systemready-ir-acs