kas: corstone1000: update for new Kas include semantics in kas folder

With Kas 2.6 included YAML files need to be relative to the repository,
not the including file:

https://kas.readthedocs.io/en/latest/format-changelog.html#version-11

Change-Id: I851c9137d1f70f754d1a70a1fc14828c39ff3de7
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>

kas/corstone1000-base.yml

@@ -1,5 +1,5 @@
 header:
-  version: 9
+  version: 11
 
 distro: poky-tiny
 

kas/corstone1000-fvp.yml

@@ -1,7 +1,7 @@
 header:
-  version: 9
+  version: 11
   includes:
-    - corstone1000-base.yml
+    - kas/corstone1000-base.yml
 
 repos:
   run-scripts:

kas/corstone1000-mps3.yml

@@ -1,6 +1,6 @@
 header:
-  version: 9
+  version: 11
   includes:
-    - corstone1000-base.yml
+    - kas/corstone1000-base.yml
 
 machine: corstone1000-mps3