Makefile: Allow 'make tests' to run tests

Add this shortcut for running tests. Unfortunately 'make test' cannot be
used as it is an existing directory.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Teddy Reed <teddy.reed@gmail.com>

Makefile

@@ -425,7 +425,7 @@ timestamp_h := include/generated/timestamp_autogenerated.h
 
 no-dot-config-targets := clean clobber mrproper distclean \
 			 help %docs check% coccicheck \
-			 ubootversion backup
+			 ubootversion backup tests
 
 config-targets := 0
 mixed-targets  := 0
@@ -1489,6 +1489,7 @@ help:
 	@echo  ''
 	@echo  'Other generic targets:'
 	@echo  '  all		  - Build all necessary images depending on configuration'
+	@echo  '  tests		  - Build U-Boot for sandbox and run tests'
 	@echo  '* u-boot	  - Build the bare u-boot'
 	@echo  '  dir/            - Build all files in dir and below'
 	@echo  '  dir/file.[oisS] - Build specified target only'
@@ -1521,6 +1522,8 @@ help:
 	@echo  'Execute "make" or "make all" to build all targets marked with [*] '
 	@echo  'For further info see the ./README file'
 
+tests:
+	$(srctree)/test/run
 
 # Documentation targets
 # ---------------------------------------------------------------------------