configs: am62x_a53_usbdfu: enable USB MASS Storage command

configs: am62x_a53_usbdfu: enable USB MASS Storage command

The USB0 instance of USB on AM62 SoC when configured to operate in the
Gadget mode of operation can be used to mount an MMC/SD card on the USB
Host. Hence, enable support for the USB Mass Storage (ums) command.

Since this config fragment corresponds to USB DFU functionality which
configures the USB Controller in Gadget mode of operation, other SoCs
which include this fragment for DFU functionality can make use of the
USB MASS Storage functionality as well.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>