power: smb135x-charger: Request HVDCP adapter to switch to 5V at shutdown

During system shutdown USB D+/D- line pull-up regulator turns off as part
of system power-off sequence. In situations when HVDCP adapter is at 9V if
voltage level of D+ line goes low, adapter treats this as a 12V request.

To prevent any erroneous request of 12V always keep HVDCP adapter at 5V
during shutdown.

CRs-Fixed: 779207
Change-Id: I338a11667f550de2ba52493173900506cbfe2d07
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>