usb: gadget: add Aspeed ast2600 udc driver

Aspeed udc is compliant with USB2.0, supports USB High Speed
and Full Speed, backward compatible with USB1.1.

Supports independent DMA channel for each generic endpoint.
Supports 32/256 stages descriptor mode for all generic endpoints.

This driver supports full functionality including single/multiple
stages descriptor mode, and exposes 1 UDC gadget driver.

Signed-off-by: Neal Liu <neal_liu@aspeedtech.com>
Link: https://lore.kernel.org/r/20220523030134.2977116-2-neal_liu@aspeedtech.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>