usb: gadget: android: Update android gadget driver

usb: gadget: android: Update android gadget driver

* Functions and the device descriptor are configured from user space:
echo 0       > /sys/class/android_usb/android0/enable
echo adb,acm > /sys/class/android_usb/android0/functions
echo 2       > /sys/class/android_usb/android0/f_acm/instances
echo 1       > /sys/class/android_usb/android0/enable

* Driver does not require platform data anymore

* Moved function initialization to android.c instead of each
function file

* Replaced switches by uevents

Signed-off-by: Benoit Goby <benoit@android.com>
Signed-off-by: Mike Lockwood <lockwood@android.com>
Change-Id: If5ad9267c111ad0a442f0d87a0d31082dc5381b6