TCPMv2: Clear pending DPMs during port discovery request
TCPMv2: Clear pending DPMs during port discovery request

If there is a pending VDM send during the processing of
DPM_REQUEST_PORT_DISCOVERY, then the VDM send and ACK may leave the DP
module in an inconsistent state.  Avoid this state by clearing any
pending VDM sends at this time.

BRANCH=None
BUG=b:182237701
TEST=on mancomb, plug in a dock in G3 and power up to S0 repeatedly,
ensuring that we can enter DP mode every time

Signed-off-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>
Change-Id: I2223ed431df97821a177e9a030b53f6310a1faf8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2912114
Reviewed-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>

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