util: Migrate chargen to python3
util: Migrate chargen to python3

BUG=chromium:1031705
BRANCH=master
TEST=Output is the same with python2

Signed-off-by: kerker <b60348db21a0b73e8345c1da67719faa1d4da16e@chromium.org>
Change-Id: Ice9bb885fe862b298c55c29c05d7f7eb4a2bead0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2425984
Reviewed-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>

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