cbfstool: Clean up code

cbfstool has diverged between coreboot upstream and the chromium tree.
Bring in some of the chromium changes, in particular the useful remainders
of cbf37fe (https://chromium-review.googlesource.com/176710)

- fix coding style
- mark unused variables explicitly unused
- remove some dead code

Change-Id: I354aaede8ce425ebe99d4c60c232feea62bf8a11
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/8577
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marc.jones@se-eng.com>

util/cbfstool/Makefile

@@ -4,8 +4,7 @@ HOSTCC ?= $(CC)
 CFLAGS ?= -g
 CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wmissing-prototypes
 CFLAGS += -Wwrite-strings -Wredundant-decls -Wno-trigraphs
-CFLAGS += -Wstrict-aliasing -Werror
-CFLAGS += -Wshadow
+CFLAGS += -Wstrict-aliasing -Wshadow -Werror
 
 CBFSTOOL_BINARY:=$(obj)/cbfstool