pd: refactor disconnection detection
pd: refactor disconnection detection

Verify the connection status at every FSM loop,
by monitoring VBUS presence for the sink and by monitoring CC going
above Vnc for the source.

Also ensure we are never stuck in the source transition state in the
sink doesn't ack the PSReady packet.

Signed-off-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

BRANCH=none
BUG=none
TEST=connect Firefly to Zinger, trigger hundreds of voltage transition,
record and analyze the PD traffic : no longer see spurious PSReady
messages.

Change-Id: I4495ae5415d53d77055fb2a562c594fa9a1d4dc8
Reviewed-on: https://chromium-review.googlesource.com/206945
Tested-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>
Reviewed-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Tested-by: Alec Berg <1a4429eeda29095a12e19a73405f80f5b7f37a63@chromium.org>
Commit-Queue: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

coreboot/chrome-ec,longsleep/ec,fourier49/BZ_DEV_EC,fourier49/BZ_DEV_EC,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,fourier49/BIZ_EC,thehobn/ec,thehobn/ec,thehobn/ec,mtk09422/chromiumos-platform-ec,longsleep/ec,akappy7/ChromeOS_EC_LED_Diagnostics,mtk09422/chromiumos-platform-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,akappy7/ChromeOS_EC_LED_Diagnostics,fourier49/BZ_DEV_EC,mtk09422/chromiumos-platform-ec,coreboot/chrome-ec,eatbyte/chromium-ec,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,md5555/ec,eatbyte/chromium-ec,md5555/ec,mtk09422/chromiumos-platform-ec,fourier49/BZ_DEV_EC,md5555/ec,fourier49/BIZ_EC,fourier49/BIZ_EC,fourier49/BIZ_EC,longsleep/ec,coreboot/chrome-ec,longsleep/ec,md5555/ec,thehobn/ec,eatbyte/chromium-ec,eatbyte/chromium-ec