usb: gadget: add udc driver for max3420

The MAX3420 is USB2.0 only, UDC-over-SPI controller. This driver
also supports the peripheral mode of MAX3421.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
3 files changed