xilinx: zynq: Add usb dfu/thor distro boot support

Add support for usb dfu & thor to distro boot on zynq platform.
Add 60s timeout of dfu-utils to start transaction. Remove
DFU_ALT_INFO_RAM as we use bootcmd_usb_dfu instead of dfu_ram.
Remove DFU_ALT_INFO_MMC as part of distro boot cleanup.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>