USB: phy-msm-usb: Disable VBUS OTG during REBOOT

Some PMICs preserve OTG state across reboots. This can
result in VBUS detection failure if target was rebooted
in host mode. To fix this make sure that VBUS OTG is
turned off during shutdown. With this PMIC boots up with
OTG (or host) mode disabled and can correctly detect VBUS
state after reboot.

CRs-fixed: 650765
Change-Id: If68bb5351577ba1020d1e88077bb9ae85654733a
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>