cr50: use the correct signer invocation options

The new signer command line option should be used by some boards, not
all of them. Add it for cr50 for now.

BRANCH=none
BUG=none
TEST=verified that --cros is added to the command line when cr50 blobs
      are signed, and that the signed blob boots fine on b1.

Change-Id: Ibc38cc6233b57838129ae7d554921c1bae0e6b8c
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/329595
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

Makefile.rules

@@ -42,7 +42,7 @@ cmd_flat_to_obj = $(CC) -T $(out)/firmware_image.lds -nostdlib $(CPPFLAGS) \
 cmd_ec_elf_to_flat ?= $(OBJCOPY) --set-section-flags .roshared=share \
 				-O binary $< $@
 cmd_elf_to_signed ?= sudo $(out)/util/signer --key=util/signer/$(3) \
-	--input=$< --format=bin --output=$@.signed \
+	--input=$< --format=bin --output=$@.signed $(SIG_EXTRA) \
 	&& sudo chown $(shell whoami) $@.signed && mv $@.signed $@
 cmd_elf_to_dis = $(OBJDUMP) -D $< > $@
 cmd_elf_to_hex = $(OBJCOPY) -O ihex $< $@

board/cr50/build.mk

@@ -16,6 +16,7 @@ CHIP_VARIANT ?= cr50_fpga
 # second time.
 ifeq ($(BOARD_MK_INCLUDED_ONCE),)
 BOARD_MK_INCLUDED_ONCE=1
+SIG_EXTRA = --cros
 else
 
 # Need to generate a .hex file