ec3po: Add USING_SUBPROCS and DoIf() to threadproc_shim.py.
ec3po: Add USING_SUBPROCS and DoIf() to threadproc_shim.py.

These are for easing the subprocesses -> threads transition across the
third_party/hdctools/ -> platform/ec/ boundary.

BRANCH=none
BUG=b:79684405
TEST="python threadproc_shim.py" executes without errors.  CL:1282265 works
correctly using the new function and constant added by this CL.

Change-Id: Iab4d12fc0565b8375a1bd1adc9a2ec5e02d85e0b
Signed-off-by: Matthew Blecker <d18f4466f2802f9c78c5c14a42b8c21fdbfabfcd@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1282012

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec