USB: configfs: Don't send DISCONNECT uevent during unbind

while testing composition switch from UI, composite driver sending
disconnect event to userspace from function unbind path or from the
bus reset. As per the none composition rules in init.msm.usb.configfs.rc
unbind should happen first and sending the disconnect event to userspace.
Userspace code will starts 1 sec timer for enumeration.

In some cases where adbd is enabled, adbd taking more than 1sec to restart
and causing delay in next composition enumeration. Another case is in RNDIS
composition switch. Where rndis function is taking more time in unbind path
and causing delay for next composition switch.

This results in userpsace timeout (1 second) causing actual composition
enumeration failure and falls back to default composition.

Workaround the issue by not sending disconnect event to userspace on
composition switch from unbind path. Instead send the disconnect event
from USB bus reset so that userspace enable timer starts from bus reset.

Change-Id: I2d1fcaa0704e369204fbba4eceb8ba9b1c525b41
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>
Signed-off-by: Pratham Pratap <prathampratap@codeaurora.org>