gitlab-ci: Build radeonsi & RADV in the ppc64el job

This requires cross-building libdrm for ppc64el.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3643>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3643>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a194d6c..508ae0d 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -483,8 +483,9 @@
     - meson-s390x
   variables:
     CROSS: ppc64el
-    GALLIUM_DRIVERS: "nouveau,swrast,virgl"
+    GALLIUM_DRIVERS: "nouveau,radeonsi,swrast,virgl"
     LLVM_VERSION: "8"
+    VULKAN_DRIVERS: "amd"
 
 meson-mingw32-x86_64:
   extends: .meson-build