gitlab-ci: Build i386 and ARM drivers in surfaceless mode.

I don't particularly care about getting x86/ARM cross-build coverage of all the window systems, but we do want to be building src/mesa/ (for x86 asm) and gallium drivers (for vc4 NEON asm). I'm also hoping to use these build products for testing freedreno on actual HW (which we do using surfaceless).

This increases the docker image from 1.4G to 1.5G. The 3 new build-test runs each took about 2 minutes of GCE time.