amdfwtool: Move some funtions to other categorized source files

To reduce the size of amdfwtool.c which is already too big.

Change-Id: Ib80eeb42f59a3dda04402b2feaadc1d178ed989e
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/73910
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>

util/amdfwtool/Makefile

@@ -9,7 +9,7 @@ endif
 
 READ_SRC = amdfwread.c
 READ_OBJ = $(READ_SRC:%.c=%.o)
-TOOL_SRC = amdfwtool.c data_parse.c
+TOOL_SRC = amdfwtool.c data_parse.c signed_psp.c handle_file.c
 TOOL_OBJ = $(TOOL_SRC:%.c=%.o)
 HEADER=amdfwtool.h
 TARGETS = amdfwread amdfwtool