AM57xx GP EVM has USB2 port of the SoC exposed as
USB client port.

It is useful to be able to use this port for USB
DFU downloads.

Enable USB DFU support. Tested on AM57x GP EVM Rev
A3 using DFU to download to connected SD card.

configs for HS version of the AM57x EVM are
included in the patch but not really tested.
Signed-off-by: NSekhar Nori <nsekhar@ti.com>
Reviewed-by: NTom Rini <trini@konsulko.com>