ci: update arm64 Travis jobs to Graviton2

Use only the newer Graviton2 environment in Travis CI instead of using
the older platform, which has intermittent issues:
1. collect2: fatal error: ld terminated with signal 9 [Killed]
2. ticketlock_autotest sometimes times out

These failures hint at resource availability issues in container
environments. The Graviton2 environment is using VMs and these failures
are not observed in it.

Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Aaron Conole <aconole@redhat.com>

.travis.yml

@@ -122,10 +122,10 @@ jobs:
           - *aarch64_clang_packages
   # aarch64 gcc jobs
   - env: DEF_LIB="static"
-    arch: arm64
+    dist: focal
-    compiler: gcc
+    arch: arm64-graviton2
-  - env: DEF_LIB="shared" RUN_TESTS=true
+    virt: vm
-    arch: arm64
+    group: edge
     compiler: gcc
   - env: DEF_LIB="shared" RUN_TESTS=true
     dist: focal
@@ -134,7 +134,10 @@ jobs:
     group: edge
     compiler: gcc
   - env: DEF_LIB="shared" BUILD_DOCS=true
-    arch: arm64
+    dist: focal
+    arch: arm64-graviton2
+    virt: vm
+    group: edge
     compiler: gcc
     addons:
       apt:
@@ -142,7 +145,10 @@ jobs:
           - *required_packages
           - *doc_packages
   - env: DEF_LIB="shared" ABI_CHECKS=true
-    arch: arm64
+    dist: focal
+    arch: arm64-graviton2
+    virt: vm
+    group: edge
     compiler: gcc
     addons:
       apt:
@@ -151,10 +157,10 @@ jobs:
           - *libabigail_build_packages
   # aarch64 clang jobs
   - env: DEF_LIB="static"
-    arch: arm64
+    dist: focal
-    compiler: clang
+    arch: arm64-graviton2
-  - env: DEF_LIB="shared" RUN_TESTS=true
+    virt: vm
-    arch: arm64
+    group: edge
     compiler: clang
   - env: DEF_LIB="shared" RUN_TESTS=true
     dist: focal