amdfwtool: Add ISH header support for A/B recovery layout

Image Slot Header (ISH) is a new feature.
The rom layout for A/B recovery with ISH:
EFS -> PSP L1 0x48 -> ISH A -> PSP L2 A -> BIOS L2 A
              0x4A -> ISH B -> PSP L2 B -> BIOS L2 B

The newer 55758 will updated about the boot priority and update retry
in ISH header.

Change-Id: Ib0690cde1dce949514c7aacebe13096b7814ceff
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57747
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

util/amdfwtool/Makefile

@@ -5,7 +5,7 @@ HOSTCC ?= cc
 SRC = amdfwtool.c data_parse.c
 OBJ = $(SRC:%.c=%.o)
 TARGET = amdfwtool
-WERROR=-Werror -Wno-unused-function
+WERROR=-Werror
 CFLAGS=-O2 -Wall -Wextra -Wshadow ${WERROR}
 
 all: $(TARGET)