qcom-charger: typec legacy cable detection

Currently the legacy cable bit is always asserted during off mode
PON via USBIN. This causes PD to be disallowed even when a
non-legacy cable is attached in off mode.

Fix this by always allowing PD upon USBIN attach PON, but keep the
normal legacy detection flow for all subsequent insertions.

CRs-Fixed: 1107607
Change-Id: I20acd75643955b6d2144389159a0dad41f01a532
Signed-off-by: Harry Yang <harryy@codeaurora.org>