util/amdfwtool: Clean up Makefile

- Add method to disable warnings as errors
- Add help target
- Add phony targets to .PHONY

BUG=None
TEST=make all; make help; make all WERROR=""

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: Icd0cfd3e2579c9016ebb616e371d1076a5a171b4
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50650
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

util/amdfwtool/Makefile

@@ -5,7 +5,8 @@ HOSTCC ?= cc
 SRC = amdfwtool.c data_parse.c
 OBJ = $(SRC:%.c=%.o)
 TARGET = amdfwtool
-CFLAGS=-O2 -Wall -Wextra -Wshadow -Werror
+WERROR=-Werror
+CFLAGS=-O2 -Wall -Wextra -Wshadow ${WERROR}
 
 all: $(TARGET)
 
@@ -19,3 +20,11 @@ clean:
 	@rm -f $(TARGET) $(OBJ)
 
 distclean: clean
+
+help:
+	@echo "${TARGET}: Create AMD Firmware combination"
+	@echo "Targets: all, clean, distclean, help"
+	@echo "To disable warnings as errors, run make as:"
+	@echo "  make all WERROR=\"\""
+
+.PHONY: all clean distclean help