ci: Move freedreno's parallelism to the runner instead of gitlab-ci jobs.

I set the runners to concurrency=1, so they serve only one gitlab-ci job
at at time.  Swap over to using the parallel runner now to keep the
runners busy, more efficiently than spawning many docker containers and
downloading artifacts multiple times, and producing easier-to-understand
results for browsing on the web.

This bumps the a306 runners to 4x parallel instead of 2x like before, but
cheza gles3 drops from 6 to 4.  Current rough timings of the jobs (if no
container download):

db410c-gles2: 5:00
a630-gles2: 1:30
a630-gles3: 6:00
a630-gles31: 5:30

a630-gles3 is a bit longer than I like, but it should come back down once
I can sort out the NIR algebraic rewinding.
39 jobs for !2837 with freedreno-ci-parallelism in 30 minutes and 33 seconds (queued for 5 seconds)
detached
Status Job ID Name Coverage
  Container
passed arm_build #993890
aarch64

00:00:21

passed arm_test #993891
aarch64

00:00:23

passed lava_arm64 #993886

00:00:20

passed lava_armhf #993885

00:00:22

passed x86_build #993887

00:00:21

passed x86_build_old #993889

00:00:21

passed x86_test #993888

00:00:20

 
  Build
passed lava-build:arm64 #993893

00:11:18

passed lava-build:armhf #993892

00:11:13

passed meson-arm64 #993897
aarch64

00:11:09

passed meson-armhf #993896
aarch64

00:06:02

passed meson-clang #993898

00:07:09

passed meson-clover #993901

00:03:33

passed meson-clover-old-llvm #993902

00:03:54

passed meson-i386 #993904

00:03:00

passed meson-main #993895

00:07:31

passed meson-mingw32-x86_64 #993905

00:03:45

passed meson-testing #993894

00:06:57

passed meson-vulkan #993903

00:03:36

passed scons #993906

00:10:57

passed scons-old-llvm #993907

00:08:31

passed scons-swr #993899

00:05:51

passed scons-win64 #993900

00:05:10

 
  Test
passed arm64_a306_gles2 #993923
db410c

00:05:50

passed arm64_a630_gles2 #993920
mesa-cheza

00:01:31

passed arm64_a630_gles3 #993922
mesa-cheza

00:06:00

passed arm64_a630_gles31 #993921
mesa-cheza

00:05:23

passed panfrost-t760-test:armhf #993908
lava-rk3288-veyron-jaq

00:05:20

passed panfrost-t860-test:arm64 #993909
lava-rk3399-gru-kevin

00:08:25

passed piglit-glslparser+quick_shader #993911

00:05:42

passed piglit-quick_gl #993910

00:08:34

passed test-llvmpipe-gles2 #993912

00:03:54

passed test-softpipe-gles2 #993913

00:01:42

passed test-softpipe-gles31 1/4 #993916

00:03:05

passed test-softpipe-gles3 1/2 #993914

00:04:38

passed test-softpipe-gles31 2/4 #993917

00:03:47

passed test-softpipe-gles31 3/4 #993918

00:05:10

passed test-softpipe-gles31 4/4 #993919

00:02:30

passed test-softpipe-gles3 2/2 #993915

00:05:43