USB: msm72k_udc: Add proprietary charger detection support

Proprietary chargers pull D+/- to specific voltages between 2.0-3.3V
(VLGC) for identification.  The DM voltage may not exceed VLGC due
to pull-down resistor.  Hence a proprietary charger is detected as
a Standard downstream port (SDP). Gadget speed is used to differentiate
between SDP and proprietary charger.

In charger detection work, if the connected charger is not SDP (or) CDP
then re-schedule the work again and if it returns invalid charger, mark
it as proprietary charger.

CRs-Fixed: 377915
Change-Id: I4223c0724c00aea7e755cd07b349c9e597d7960d
Signed-off-by: Chiranjeevi Velempati <cvelempa@codeaurora.org>