[DRIVERS] usb: Improve usb_control_msg() and usb_set_address()

Signed-off-by: Anup Patel <anup@brainfault.org>
[DRIVERS] usb: Add header for virtual root hub descriptors

Quite a few USB host controllers don't have root hub as separate
device. Instead for such devices we need to emulate root hub
device using register accesses.

This patch adds header file for assisting USB host controller
driver in emulating virtual root hub.

Signed-off-by: Anup Patel <anup@brainfault.org>