rp2: Allow extra arguments in Makefile.

When building allow the port to be configured on the command line by
passing a value for CMAKE_ARGS.

Signed-off-by: Peter Harper <peter.harper@raspberrypi.com>

Author: peterharperuk

ports/rp2/Makefile

@@ -30,26 +30,26 @@ endif
 
 $(VERBOSE)MAKESILENT = -s
 
-CMAKE_ARGS += -DMICROPY_BOARD=$(BOARD) -DMICROPY_BOARD_DIR="$(abspath $(BOARD_DIR))"
+override CMAKE_ARGS += -DMICROPY_BOARD=$(BOARD) -DMICROPY_BOARD_DIR="$(abspath $(BOARD_DIR))"
 
 ifdef USER_C_MODULES
-CMAKE_ARGS += -DUSER_C_MODULES=${USER_C_MODULES}
+override CMAKE_ARGS += -DUSER_C_MODULES=${USER_C_MODULES}
 endif
 
 ifneq ($(FROZEN_MANIFEST),)
-CMAKE_ARGS += -DMICROPY_FROZEN_MANIFEST=${FROZEN_MANIFEST}
+override CMAKE_ARGS += -DMICROPY_FROZEN_MANIFEST=${FROZEN_MANIFEST}
 endif
 
 ifeq ($(DEBUG),1)
-CMAKE_ARGS += -DCMAKE_BUILD_TYPE=Debug
+override CMAKE_ARGS += -DCMAKE_BUILD_TYPE=Debug
 endif
 
 ifdef BOARD_VARIANT
-CMAKE_ARGS += -DMICROPY_BOARD_VARIANT=$(BOARD_VARIANT)
+override CMAKE_ARGS += -DMICROPY_BOARD_VARIANT=$(BOARD_VARIANT)
 endif
 
 ifdef MICROPY_PREVIEW_VERSION_2
-CMAKE_ARGS += -DMICROPY_PREVIEW_VERSION_2=1
+override CMAKE_ARGS += -DMICROPY_PREVIEW_VERSION_2=1
 endif
 
 HELP_BUILD_ERROR ?= "See \033[1;31mhttps://github.com/micropython/micropython/wiki/Build-Troubleshooting\033[0m"