cmocka/test-all-defconfig.sh: add banners between platforms

Sample output:

[ 97%] Built target acos_32b_fixed
[ 98%] Linking C executable volume_process
[ 98%] Built target volume_process
[100%] Linking C executable strcheck
[100%] Built target strcheck

    =========  Building cmocka tests for broadwell_defconfig ======

+ cmake -DINIT_CONFIG=broadwell_defconfig -S /srv/mherber2/SOFub20/sof
   -B build_ut_defs/broadwell_defconfig -DBUILD_UNIT_TESTS=ON
   -DBUILD_UNIT_TESTS_HOST=ON

-- version.cmake starting SOF build at 2021-12-17T01:09:44Z UTC
-- Building git commit with parent(s):

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

test/test-all-defconfigs.sh

@@ -12,6 +12,8 @@ rebuild_config()
 {
     local conf="$1"
     mkdir -p "$BUILDTOP"
+    printf '\n    =========  Building native cmocka tests for %s ======\n\n' "$conf"
+
     ( set -x
      cmake  -DINIT_CONFIG="$conf" -S "$SOFTOP" -B "$BUILDTOP"/"$conf" \
             -DBUILD_UNIT_TESTS=ON           \
@@ -33,6 +35,7 @@ main()
 
     # Now run all the tests
     for d in "$BUILDTOP"/*_defconfig; do
+        printf '\n\n    =========  Running native cmocka tests in %s ======\n\n' "$d"
         ( set -x
          cmake --build "$d" -- test
         )