usb: pd: Fix sink hard reset timing

The current hard reset handling (most recently fixed with
commit 172cec3a ("usb: pd: Improve sink hard reset handling"))
is based on a maximum timeout for the longest possible (according
to spec) duration that VBUS may turn off and back on again, just
under 2s, before re-starting the sink and waiting for capabilities
again. However, this method is prone to timing errors, particularly
tTypeCSinkWaitCap, which should be based on when VBUS turns on.

Fix this by making use of the VBUS presence notification from the
charger (PROP_PRESENT). Keep track of this in the psy_changed()
callback and use the falling notification to determine when to
transition out of PE_SNK_TRANSITION_TO_DEFAULT into PE_SNK_STARTUP.
Bring back PE_SNK_DISCOVERY which is now used as a waiting state
until the VBUS rising notification comes and transition to
PE_SNK_WAIT_FOR_CAPABILITIES. And move setting of PROP_VOLTAGE_MAX
to PE_SNK_STARTUP after VBUS has turned off to avoid tripping
the charger's overvoltage detection.

Also since aforementioned commit, the CC HW is now able to handle
VBUS going away and not treating it as a false disconnect, so we
can remove the workaround as a disconnect can now be treated as
a disconnect.

Change-Id: I885f3f4c219e102758fd09c8aae9257d093ebb72
Signed-off-by: Jack Pham <jackp@codeaurora.org>