ci/bare-metal: Pass through FDO_CI_CONCURRENT on bare-metal runners.

I've set it up in the gitlab-runer config on all the freedreno boards.
This means that for piglit, where the run.sh always choose either this
variable or 4 threads otherwise, we'll have the right number of parallel
tasks.

Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7370>

.gitlab-ci.yml

@@ -1538,6 +1538,7 @@ arm64_a306_gles3_options:
     # Disable SMP because only CPU 0 is at a freq higher than 19mhz on
     # current upstream kernel.
     BM_CMDLINE: "ip=dhcp console=ttyMSM0,115200n8 nosmp"
+    FDO_CI_CONCURRENT: 1
     GPU_VERSION: freedreno-a530
     DEQP_EXPECTED_RENDERER: FD530
   tags:

.gitlab-ci/bare-metal/rootfs-setup.sh

@@ -43,6 +43,7 @@ for var in \
     DEVICE_NAME \
     DRIVER_NAME \
     EGL_PLATFORM \
+    FDO_CI_CONCURRENT \
     FDO_UPSTREAM_REPO \
     FD_MESA_DEBUG \
     FLAKES_CHANNEL \

docs/ci/bare-metal.rst

@@ -116,7 +116,10 @@ required by your bare-metal script, something like::
 
   [[runners]]
     name = "google-freedreno-db410c-1"
-    environment = ["BM_SERIAL=/dev/ttyDB410c8", "BM_POWERUP=google-power-up.sh 8", "BM_FASTBOOT_SERIAL=15e9e390"]
+    environment = ["BM_SERIAL=/dev/ttyDB410c8", "BM_POWERUP=google-power-up.sh 8", "BM_FASTBOOT_SERIAL=15e9e390", "FDO_CI_CONCURRENT=4"]
+
+The ``FDO_CI_CONCURRENT`` variable should be set to the number of CPU threads on
+the board, which is used for auto-tuning of job parallelism.
 
 If you want to collect the results for fastboot you need to add the following
 two board-specific environment variables ``BM_WEBDAV_IP`` and ``BM_WEBDAV_PORT``.