[AOA FFS Implementation] Start vendor control monitor

Open the new FFS function within ctrl directory, write the correct
strings and descriptors to it, start the vendor control monitor to
monitor requests on this ep0 and handle vendor control requests in the
thread.

Bug: 407985367
Bug: 421817435
Flag: android.hardware.usb.flags.enable_aoa_userspace_implementation
Test: Built and installed the system image on a device. Verified that the functionfs driver could setup FFS to monitor vendor control request.
Test: Verified the accessory mode control request could be sent to userspace and handled.
Change-Id: Ic78ef6bad037522d4f9d5795b5fcefbc85034293