arm: socfpga: de0_nano: Probe DWC2 UDC from OF instead of hard-coded data

This patch adds the necessary OF alias for the UDC node, which let's
the code locate the DWC2 UDC base address in OF instead of hard-coding
it into the U-Boot binary. The code is adjusted to use the address from
OF instead of the hard-coded one. Finally, the hard-coded address is
removed and USB DM support is enabled.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Lukasz Majewski <l.majewski@majess.pl>
Cc: Lukasz Majewski <l.majewski@samsung.com>

arch/arm/dts/socfpga_cyclone5_de0_nano_soc.dts

@@ -16,6 +16,7 @@
 
 	aliases {
 		ethernet0 = &gmac1;
+		udc0 = &usb1;
 	};
 
 	memory {
@@ -59,3 +60,7 @@
 	status = "okay";
 	u-boot,dm-pre-reloc;
 };
+
+&usb1 {
+	status = "okay";
+};