usb: bdc: fix "xsf for ep not enabled" errror

This patch essentially clears the port status change bits at the
correct times. It is necessary because the driver was not handling
the change bits correctly for events during device
connection/disconnection and bus enumeration. So, one of them (PCC)
was left stuck sometimes causing the "xsf for ep not enabled"
error we get on first connection. This was found by the Android team.
This was debugged and fixed by Sasi Kumar.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>