Makefile: Add unit-tests help and targets list

Add unit-tests targets to help output. Add list-unit-tests target
that lists all available unit-tests.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: I464a76cbea1f4afbc3fc772960787952e61b95b9
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52293
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>
diff --git a/tests/Makefile.inc b/tests/Makefile.inc
index 027091c..48bd18b 100644
--- a/tests/Makefile.inc
+++ b/tests/Makefile.inc
@@ -179,3 +179,18 @@
 
 clean-unit-tests:
 	rm -rf $(testobj)
+
+list-unit-tests:
+	@echo "unit-tests:"
+	for t in $(sort $(alltests)); do \
+		echo "  $$t"; \
+	done
+
+help-unit-tests help::
+	@echo  '*** coreboot unit-tests targets ***'
+	@echo  '  unit-tests        - Run all unit-tests from tests/'
+	@echo  '  clean-unit-tests  - Remove unit-tests build artifacts'
+	@echo  '  list-unit-tests   - List all unit-tests'
+	@echo  '  <unit-test>       - Build and run single unit-test'
+	@echo  '  clean-<unit-test> - Remove single unit-test build artifacts'
+	@echo