ci/b2c: allow using another initrd that contains firmware

This allows DUTs that require firmware to boot reliably to provide them
without needing to include them in the kernel image.

Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>
Reviewed-by: Eric Engestrom <None>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33162>

.gitlab-ci/b2c/b2c.yml.jinja2.jinja2

@@ -98,9 +98,14 @@ deployment:
         {{ kernel_cmdline_extras }}
         {% endif %}
 
-{% if initramfs_url %}
+{% if initramfs_url or firmware_url %}
     initramfs:
-      url: '{{ initramfs_url }}'
+{% if firmware_url %}
+      - url: '{{ firmware_url }}'
+{% endif %}
+{% if initramfs_url %}
+      - url: '{{ initramfs_url }}'
+{% endif %}
 {% endif %}
 
 {% if dtb_url %}