Add support for toplevel Makefile

Add toplevel Makefile with clean support.
Updated Readme for building details.

Author: disdi

Makefile

@@ -0,0 +1,11 @@
+CODE_DIR = customer_app
+
+.PHONY: app
+
+app:
+	$(MAKE) -C $(CODE_DIR)
+clean:
+	find . -name build_out|xargs rm -rf
+	find . -name __pycache__|xargs rm -rf
+	find . -type f -name "*.pyc" -delete
+	rm -rf tools/sdk_pub_tool/bouffalolab*

README.rst

@@ -18,18 +18,22 @@ You can find a lot of documentation on `PINE64 Documentation Website <https://pi
 
 Quick Start
 -----------
-In order to build one of the sample apps, you need to set a few environment
-variables::
+In order to build sample apps, you need to set a few environment variables::
 
     export BL60X_SDK_PATH=/path/to/this/repo
     export CONFIG_CHIP_NAME=BL602
 
-Then go to the sample directory of interest and call `make`, for example::
+In order to build all sample apps simply call `make`, for example ::
+    make
+
+To only build the sample app of interest, go to the directory of the app,
+then call `make`, for example::
 
     cd customer_app/bl602_boot2
     make
 
 Call ::
+=======
 
     make CONFIG_TOOLPREFIX=riscv64-linux-gnu-
 

clean

@@ -2,3 +2,5 @@
 
 app:
 	find . -maxdepth 2 -mindepth 2 -type d -execdir ./genromap {} \;
+clean:
+	find . -name build_out|xargs rm -rf