ANDROID: usb: gadget: configfs: Add Uevent to notify userspace

Android userspace UsbDeviceManager relies on the uevents generated
by the composition driver to generate user notifications. Therefore,
uevents will be generated whenever USB changes its state. This patch
also add "state" attribute to android_device to show USB state. In
addition, this patch adds android_create_function_device to create child
function devices for USB gadget functions as well as
android_remove_function_device to remove them. Android UsbDeviceManager
relies on communicating to the devices created by the gadget functions
to implement functions such as midi.

Bug: 120441124
Bug: 317149848
Signed-off-by: Neill Kapron <nkapron@google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:847539d9ef441cfe423809f2992c7b7a554c924f)
Merged-In: I471772a2514568dd7f2b2a0316a5f018b3b378ed
Change-Id: I471772a2514568dd7f2b2a0316a5f018b3b378ed