util: update flash_ec to handle unibuild emerge paths

If a baseboard exists in the build.mk for a board, use that
as the unibuild path.

BRANCH=none
BUG=b:77128456
TEST=tested the following command with correct results:
	    flash_ec --board=yorp  (baseboard)
	    flash_ec --board=bip   (baseboard)
	    flash_ec --board=grunt (non-baseboard)

Change-Id: Ic4573cb01849275d1333ff9e715f69a4c95444b0
Signed-off-by: Jett Rink <jettrink@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/986753
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

Makefile.rules

@@ -463,6 +463,10 @@ flash_ec: $(out)/ec.bin
 flash_dfu: $(out)/ec.bin
 	sudo ./$(BDIR)/dfu $(out)/ec.bin
 
+.PHONY: print-baseboard
+print-baseboard:
+	@echo "${BASEBOARD}"
+
 .PHONY: clean
 clean:
 	-rm -rf $(out)

util/flash_ec

@@ -222,7 +222,6 @@ function get_servo_type() {
 }
 
 BOARD=${FLAGS_board}
-BOARD_ROOT=/build/${BOARD}
 
 in_array() {
 	local n=$#
@@ -412,13 +411,21 @@ else
 	EC_FILE=ec.bin
 fi
 
-EMERGE_BUILD=${BOARD_ROOT}/firmware/${EC_FILE}
 
 LOCAL_BUILD=
 if [[ -n "${EC_DIR}" ]]; then
 	LOCAL_BUILD="${EC_DIR}/build/${BOARD}/${EC_FILE}"
 fi
 
+# Get baseboard from build system if present
+BASEBOARD=$(make --quiet -C ${EC_DIR} BOARD=${BOARD} print-baseboard)
+
+if [[ -n "${BASEBOARD}" ]]; then
+	EMERGE_BUILD=/build/${BASEBOARD}/firmware/${BOARD}/${EC_FILE}
+else
+	EMERGE_BUILD=/build/${BOARD}/firmware/${EC_FILE}
+fi
+
 # Find the EC image to use
 function ec_image() {
 	# No image specified on the command line, try default ones