tests: lm32: new rule for single test cases

Introduce new target "check_%" to run individual test caes, eg.
  make check_mmu
Signed-off-by: NMichael Walle <michael@walle.cc>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>

tests/tcg/lm32/Makefile

@@ -96,10 +96,10 @@ all: build
 
 build: $(CRT) $(TESTCASES)
 
-check: $(CRT) $(SYS) $(TESTCASES)
-	@for case in $(TESTCASES); do \
-		$(SIM) $(SIMFLAGS) ./$$case; \
-	done
+check: $(TESTCASES:test_%.tst=check_%)
+
+check_%: test_%.tst $(CRT) $(SYS)
+	$(SIM) $(SIMFLAGS) $<
 
 clean:
 	$(RM) -fr $(TESTCASES) $(CRT)