USB: msm72k_udc: Disable non-std charger feature by default & add debugfs

Add non-standard(proprietary) charger feature only for qrd7627a and
disable it by default and add a debugfs entry to enable it during
runtime if required using the following command:

echo 1 > /sys/kernel/debug/msm_hsusb/proprietary_chg

CRs-Fixed: 390597
CRs-Fixed: 386232
Change-Id: I19da908d11ff7c98327597b3375bf4d0a6122abc
Signed-off-by: Rajkumar Raghupathy <raghup@codeaurora.org>