fvp_utils: support trace-based code coverage in FVP LAVA jobs

Different test configurations required the trace-based code
coverage pluging [1], however in OpenCI, these are disabled due to
lack of support. This commit enables the support in LAVA jobs,
fetching the coverage trace plugin from the downloads repository
[2]. This patch co-depends on [3] to properly work.

NOTE: this patch does not cover the extraction of trace logs from LAVA
into Jenkins, so the latter can convert logs into human-friendly LCOV
html reports. This is WIP and will be coverered in a separate patch.

[1] https://gitlab.arm.com/tooling/qa-tools
[2] https://downloads.trustedfirmware.org
[3] https://review.trustedfirmware.org/c/ci/tf-a-job-configs/+/9631

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I20c1cb0570169dad1e4c3fd8b6245c820cf5d1ac
diff --git a/utils.sh b/utils.sh
index 51e3178..6a5ce49 100644
--- a/utils.sh
+++ b/utils.sh
@@ -326,7 +326,7 @@
 spm_src_repo_url="${spm_src_repo_url:-$SPM_SRC_REPO_URL}"
 spm_src_repo_url="${spm_src_repo_url:-https://$tforg_gerrit_url/hafnium/hafnium}"
 
-# FIXME set a sane default for tfa_downloads
+tf_downloads="${tf_downloads:-file:///downloads/}"
 tfa_downloads="${tfa_downloads:-file:///downloads/tf-a}"
 css_downloads="${css_downloads:-$tfa_downloads/css}"