configs: am62px_evm_a53_defconfig: enable USB DFU support

configs: am62px_evm_a53_defconfig: enable USB DFU support

The config fragment "am62x_a53_usbdfu.config" which adds USB DFU support
for AM62x SoC is applicable to the AM62Px SoC as well. Hence, include it
in "am62px_evm_a53_defconfig" in order to enable support for USB DFU
flash and boot. Remove those configs from "am62px_evm_a53_defconfig" which
are present in the "am62x_a53_usbdfu.config" config fragment that is being
included.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>