tcpm: fusb302: Don't mistake meaningful packets for GOOD_CRC
tcpm: fusb302: Don't mistake meaningful packets for GOOD_CRC

If a partner port sends a packet at approximately the same time as we
send a packet, we may end up with the initial packet followed by the
GOOD_CRC reply in our HW FIFO. Don't automatically discard the first
packet in the FIFO. Instead, discard the packet only if it's a GOOD_CRC
packet. And, modify our get_message function to automatically discard
GOOD_CRC in search of a meaningful packet.

In addition, due to interrupt latency, we can't rely on receiving one
interrupt per incoming packet. If our Rx FIFO is non-empty, assume that
it contains at least one packet.

BUG=chrome-os-partner:60242
BRANCH=gru
TEST=Manual on kevin, attach Apple dongle with no inputs. Attach zinger,
verify we negotiate to ~20V. Repeat 10x and verify negotiation is
successful each time.

Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Change-Id: I7e4430fc2b7ed44b1aa4b561d72c8e1e964b245a
Reviewed-on: https://chromium-review.googlesource.com/414927
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
(cherry picked from commit 373f5dfd75e8ea5074d26fc6392eafe83de4f905)
Reviewed-on: https://chromium-review.googlesource.com/419186
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>

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