ci/freedreno: do not build tools executables without explicitly enabling them

If the ASAN build is enabled (with libxml2 available and freedreno not listed in tools), it will result in an ASAN failure.

Job: https://gitlab.freedesktop.org/okias/mesa/-/jobs/38353567#L1521

FAILED: src/freedreno/afuc/afuc_test.fw 
/builds/okias/mesa/_build/src/freedreno/afuc/afuc-asm -g 6 ../src/freedreno/afuc/../.gitlab-ci/traces/afuc_test.asm src/freedreno/afuc/afuc_test.fw
==7765==ASan runtime does not come first in initial library list; you should either link runtime to your application or manually preload it with LD_PRELOAD.

Despite the ASAN failure, this merge request ensures that the build behaves consistently and independently of the availability of libxml2.