flashrom.c: Move read_buf_from_file() to helpers_fileio.c

Constructing a buffer from a read file is auxiliary
functionality to the core flashrom algorithms. Move
aside to decrease the overall complexity of flashrom.c

Change-Id: Ia6e1eeb876722899defb5b75346d1f22c70bfbd1
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/66645
Original-Reviewed-by: Evan Benn <evanbenn@google.com>
Original-Reviewed-by: Sam McNally <sammc@google.com>
Original-Reviewed-by: Nico Huber <nico.h@gmx.de>
Original-Reviewed-by: Thomas Heijligen <src@posteo.de>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72347
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/Makefile b/Makefile
index 213cfc2..74bacaa 100644
--- a/Makefile
+++ b/Makefile
@@ -388,7 +388,7 @@
 # Library code.
 
 LIB_OBJS = libflashrom.o layout.o flashrom.o udelay.o programmer.o programmer_table.o \
-	helpers.o ich_descriptors.o fmap.o platform/endian_$(ENDIAN).o platform/memaccess.o
+	helpers.o helpers_fileio.o ich_descriptors.o fmap.o platform/endian_$(ENDIAN).o platform/memaccess.o
 
 
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