usb: gadget: android: Add minimum delay between disconnect and connect

Some controller hardware, such as DWC3, need a minimum delay
between removing and re-applying the pullups in order for the
host to properly detect a soft disconnect and for subsequent
re-enumeration to succeed. Keep track of the last time
android_disable() was called and delay if necessary so that enough
time will have elapsed before calling usb_gadget_connect() from
android_enable().

Change-Id: I43ba441af7c7f1ea2ffe8547df5f004fbf07c823
Signed-off-by: Jack Pham <jackp@codeaurora.org>