pd: Check for dual-role partner when TOGGLE_OFF/FORCE_SINK

Charging via hub with the ANX3429 TCPC sometimes fails when the system
is in S5/G3. Both the hub and the ANX3429 are auto-toggling, so source
and sink roles depend on the timing of the connection. Charging will
fail when the hub expects the ANX3429 to be a source, but the
drp_state in S5/G3 is TOGGLE_OFF/FORCE_SINK.

Ideally we wouldn't use auto-toggle when drp_state is
TOGGLE_OFF/FORCE_SINK, but with the ANX3429 TCPC, auto-toggle can't be
prevented in low power mode.

To fix this, try being a sink in case the connected device is dual-role.
100 ms is enough time for a dual-role partner to switch from sink to
source. If the connected device is sink-only, then we will attempt
SNK_DISCONNECTED twice (due to debounce time), then return to low power
mode (and stay there). After 200 ms, reset ready for a new connection.

Move the next_state selection out into a function since things were
getting very narrow inside PD_STATE_DRP_AUTO_TOGGLE.

BRANCH=none
BUG=b:72007056
TEST=sink device + ANX3429: low power mode
TEST=sink device + PS8751: low power mode
TEST=charger via hub + ANX3429: starts charging (20/20 tries)
TEST=charger via hub + PS8751: starts charging
(all tests with Grunt in G3)

Change-Id: I097dcace96bc6e6e9cfab279bcbded50ef9951e3
Signed-off-by: Edward Hill <ecgh@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1194678
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Reviewed-by: Jett Rink <jettrink@chromium.org>

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