TARGET=zephyr_no_ddr is broken; cannot import name 'csr_map_update' from 'targets.utils'

[tcal-x]

I initialized with

export CPU=vexriscv
export CPU_VARIANT=full
export PLATFORM=arty
export FIRMWARE=zephyr
export TARGET=zephyr_no_ddr

and saw this when I tried to build the gateware:

(LX P=arty T=zephyr_no_ddr C=vexriscv.full F=zephyr) tim@tim-ubuntu:~/timvideos/litex-buildenv$ make gateware
mkdir -p build/arty_zephyr_no_ddr_vexriscv.full
time python -u ./make.py --platform=arty --target=zephyr_no_ddr --cpu-type=vexriscv --iprange=192.168.100   --cpu-variant=full --cpu-variant=full  \
        2>&1 | tee -a /home/tim/timvideos/litex-buildenv/build/arty_zephyr_no_ddr_vexriscv.full/output.20210513-162617.log; (exit ${PIPESTATUS[0]})
Traceback (most recent call last):
  File "./make.py", line 185, in <module>
    main()
  File "./make.py", line 123, in main
    soc = get_soc(args, platform)
  File "./make.py", line 56, in get_soc
    exec("from targets.{}.{} import SoC".format(args.platform, args.target.lower(), args.target), globals())
  File "<string>", line 1, in <module>
  File "/home/tim/timvideos/litex-buildenv/targets/arty/zephyr_no_ddr.py", line 15, in <module>
    from targets.utils import csr_map_update, period_ns
ImportError: cannot import name 'csr_map_update' from 'targets.utils' (/home/tim/timvideos/litex-buildenv/targets/utils.py)

real    0m0.093s
user    0m0.090s
sys     0m0.005s
make: *** [Makefile:272: gateware] Error 1

I don't think FIRMWARE=zephyr makes a difference, since I saw the same error when FIRMWARE was empty.