Reduced build sources to just the core littlefs

Currently this is just lfs.c and lfs_util.c. Previously this included
the block devices, but this meant all of the scripts needed to
explicitly deselect the block devices to avoid reporting build
size/coverage info on them.

Note that test.py still explicitly adds the block devices for compiling
tests, which is their main purpose. Humorously this means the block
devices will probably be compiled into most builds in this repo anyways.

scripts/test.py

@@ -22,17 +22,20 @@ import signal
 
 TEST_PATHS = 'tests'
 RULES = """
+# add block devices to sources
+TESTSRC ?= $(SRC) $(wildcard bd/*.c)
+
 define FLATTEN
 %(path)s%%$(subst /,.,$(target)): $(target)
     ./scripts/explode_asserts.py $$< -o $$@
 endef
-$(foreach target,$(SRC),$(eval $(FLATTEN)))
+$(foreach target,$(TESTSRC),$(eval $(FLATTEN)))
 
 -include %(path)s*.d
 .SECONDARY:
 
 %(path)s.test: %(path)s.test.o \\
-        $(foreach t,$(subst /,.,$(SRC:.c=.o)),%(path)s.$t)
+        $(foreach t,$(subst /,.,$(TESTSRC:.c=.o)),%(path)s.$t)
     $(CC) $(CFLAGS) $^ $(LFLAGS) -o $@
 
 # needed in case builddir is different