TCPMv2: Hard reset when we've dropped Vconn

Many Chromebooks will stop sourcing Vconn in G3, and don't have
sufficient notice during chipset transitions to properly swap Vconn back
to the partner before it is dropped.  For these cases, send a hard reset
in order to move the role of Vconn supplier back to the source.

Note that some boards use GPIO checks to verify whether they can source
Vconn, and these could take some amount of time after G3 entry to
settle.

BRANCH=None
BUG=b:199044441
TEST=on guybrush, attach a charger which will not swap Vconn and observe
no hard resets are sent in G3.  Attach charger which does Vconn swap and
observe a hard reset is sent, and the cable is probed once the system is
powered on again.

Signed-off-by: Diana Z <dzigterman@chromium.org>
Change-Id: Ia1c9533c36c6c7a650109182c5adf8444ffde43a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3161320
Tested-by: Li Feng <li1.feng@intel.com>
Reviewed-by: Denis Brockus <dbrockus@chromium.org>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Abe Levkoy <alevkoy@chromium.org>

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