CI: Add Aspeed AST2600

The AST2600 has a Qemu model that allows testing. Create a SPI NOR image
containing the combined SPL and u-boot FIT image.

Reviewed-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>

.gitlab-ci.yml

@@ -272,6 +272,12 @@ evb-ast2500 test.py:
     TEST_PY_ID: "--id qemu"
   <<: *buildman_and_testpy_dfn
 
+evb-ast2600 test.py:
+  variables:
+    TEST_PY_BD: "evb-ast2600"
+    TEST_PY_ID: "--id qemu"
+  <<: *buildman_and_testpy_dfn
+
 sandbox_flattree test.py:
   variables:
     TEST_PY_BD: "sandbox_flattree"