test: add repeating deferred test
test: add repeating deferred test

Adding simple unit test that ensures that a deferred call can call
itself and won't repeat forever. I thought this might be a problem, but
it wasn't. We might as well add this code as a unit test.

BRANCH=none
BUG=none
TEST=test passes

Change-Id: Ie9791606e4a401821594df122481f22d87eadbbd
Signed-off-by: Jett Rink <9d4aef0593e6843318d99df31597fb6153b89787@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2025073
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

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