VAR-SOM-AM33 USB OTG host

Change USB-OTG port configuration to Host-only

From SW perspective, the developer should do as follows:

• Download a VAR-SOM-AM33 kernel out-of-tree.
• Update var-som-am33.dts, as follows:

$ gedit arch/arm/boot/dts/var-som-am33.dts
...
           usb@47401800 {
                               status = "okay";
                               dr_mode = "host"; /* <<-- Add this line */
                        };
...

• Build var-som-am33.dtb and replace it on flash / NFS.

Once the var-som-am33.dtb has been replaced on flash / NFS - The USB-OTG port will function in Host-only mode.