feat(stablediffusion-ggml): build a ROCm variant (#11774)

The Makefile already had a hipblas branch, but no CI row built it and
the gallery's `amd:` mapping stayed commented out. On an AMD host the
capability lookup found no `amd` key and fell back to `default`, so
these users silently ran the CPU build.

Add the hipblas row to the backend matrix and the two gallery entries
it publishes, then point `amd:` at them.

Drop `-DGGML_HIPBLAS=ON` while here. `SD_HIPBLAS` sets `GGML_HIP`
itself, and `GGML_HIPBLAS` is the name ggml used before the rename, so
the flag only produced an unused-variable warning. Add gfx1151 to the
local target list to match the value the workflows pass in.


Assisted-by: Claude Code:claude-opus-5[1m]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

.github/backend-matrix.yml

@@ -3754,6 +3754,19 @@ include:
     dockerfile: "./backend/Dockerfile.golang"
     context: "./"
     ubuntu-version: '2404'
+  - build-type: 'hipblas'
+    cuda-major-version: ""
+    cuda-minor-version: ""
+    platforms: 'linux/amd64'
+    tag-latest: 'auto'
+    tag-suffix: '-gpu-rocm-hipblas-stablediffusion-ggml'
+    runs-on: 'ubuntu-latest'
+    base-image: "rocm/dev-ubuntu-24.04:7.2.1"
+    skip-drivers: 'false'
+    backend: "stablediffusion-ggml"
+    dockerfile: "./backend/Dockerfile.golang"
+    context: "./"
+    ubuntu-version: '2404'
   - build-type: 'sycl_f16'
     cuda-major-version: ""
     cuda-minor-version: ""