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>

drivers/usb/gadget/udc/Kconfig

@@ -441,6 +441,16 @@ config USB_GADGET_XILINX
 	  dynamically linked module called "udc-xilinx" and force all
 	  gadget drivers to also be dynamically linked.
 
+config USB_MAX3420_UDC
+	tristate "MAX3420 (USB-over-SPI) support"
+	depends on SPI
+	help
+	  The Maxim MAX3420 chip supports USB2.0 full-speed peripheral mode.
+	  The MAX3420 is run by SPI interface, and hence the dependency.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called max3420_udc
+
 config USB_TEGRA_XUDC
 	tristate "NVIDIA Tegra Superspeed USB 3.0 Device Controller"
 	depends on ARCH_TEGRA || COMPILE_TEST

drivers/usb/gadget/udc/Makefile

@@ -42,3 +42,4 @@ obj-$(CONFIG_USB_GADGET_XILINX)	+= udc-xilinx.o
 obj-$(CONFIG_USB_SNP_UDC_PLAT) += snps_udc_plat.o
 obj-$(CONFIG_USB_ASPEED_VHUB)	+= aspeed-vhub/
 obj-$(CONFIG_USB_BDC_UDC)	+= bdc/
+obj-$(CONFIG_USB_MAX3420_UDC)	+= max3420_udc.o