drm_hwcomposer: Tidy-up the CI scripts

1. Use -Wextra instead of multiple -Wxxx arguments. It will turn on remaining
   checks (such as -Wunused-parameter, which is currently disabled in CI)

2. Bump-up ANDROID_API definitions to 31

3. Fix clang-format-diff-X version to match the one specified in the README.md

Signed-off-by: Roman Stratiienko <roman.o.stratiienko@globallogic.com>
diff --git a/.ci/.gitlab-ci-checkcommit.sh b/.ci/.gitlab-ci-checkcommit.sh
index 817afa7..e59ad9f 100755
--- a/.ci/.gitlab-ci-checkcommit.sh
+++ b/.ci/.gitlab-ci-checkcommit.sh
@@ -50,7 +50,7 @@
 		exit 1
 	fi
 
-	git show "$h" -- | clang-format-diff-11 -p 1 -style=file > /tmp/format-fixup.patch
+	git show "$h" -- | clang-format-diff-12 -p 1 -style=file > /tmp/format-fixup.patch
 	if [ -s  /tmp/format-fixup.patch ]; then
 		cat /tmp/format-fixup.patch >&2
 		exit 1