tcpc: change pd_tx_done() to only wait for DMA done event
tcpc: change pd_tx_done() to only wait for DMA done event

Change pd_tx_done() to wait specifically for the DMA complete
event using task_wait_event_mask().

This fixes a potential bug where if we get another event, for
example a TCPM event, while waiting for transmit to complete
we restore the pending event after we are done.

BUG=none
BRANCH=smaug
TEST=run on glados and make a bunch of contracts with zinger.

Change-Id: Ie28d97eba3edcc7a98fe842e8b7eb6b9d7707047
Signed-off-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/277297
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

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