util/cbfstool: Update Makefiles

- Add a distclean target
- Add a help target
- Add the -Wshadow option

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: Ie31d61bd0e28b1e228656dfa09b5ab1996868706
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50848
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

util/cbfstool/Makefile.inc

@@ -87,7 +87,7 @@ amdcompobj += elfheaders.o
 amdcompobj += common.o
 amdcompobj += xdr.o
 
-TOOLCFLAGS ?= -Werror -Wall -Wextra
+TOOLCFLAGS ?= -Werror -Wall -Wextra -Wshadow
 TOOLCFLAGS += -Wcast-qual -Wmissing-prototypes -Wredundant-decls -Wshadow
 TOOLCFLAGS += -Wstrict-prototypes -Wwrite-strings
 TOOLCFLAGS += -O2