usb-detector: Add UsbPortDbus property

Add UsbPortDbus property which is a normalized version of UsbPort (replacing non-alphanumeric/underscore characters with underscores). This is used for D-Bus path construction in Entity-Manager to avoid path mismatches, while keeping UsbPort in its original format for sysfs lookup.

Tested: Built and verified.
Google-Bug-Id: 536095010
Change-Id: Ic9ba8193c962448231989f7de3adb8fc80358755
Signed-off-by: Guangzong Chen <guangzong@google.com>
TAG=agy
CONV=73f88cc8-43e3-450d-b174-1a11d58204ba