Adding board scratch space.

- Including ability to define custom defaults as char[] that is baked into the build
- removed unnecessary size of custom defaults header parsing (defines provided by build process or in board.h for devs).

Makefile

@@ -17,6 +17,7 @@
 
 # The target to build, see VALID_TARGETS below
 TARGET    ?= STM32F405
+BOARD     ?= 
 
 # Compile-time options
 OPTIONS   ?=
@@ -100,6 +101,11 @@ FEATURES        =
 FEATURE_CUT_LEVEL_SUPPLIED := $(FEATURE_CUT_LEVEL)
 FEATURE_CUT_LEVEL =
 
+ifneq ($(BOARD),)
+# silently ignore if the file is not present. Allows for target defaults.
+-include $(ROOT)/src/main/board/$(BOARD)/board.mk
+endif
+
 include $(ROOT)/make/targets.mk
 
 REVISION := norevision