cmd: fpga: Remove fit image support passed without fpga device

cmd: fpga: Remove fit image support passed without fpga device

The patch applied in 2010
"cmd_fpga: cleanup help and check parameters"
(sha1: a790b5b2326be9d7c9ad9e3d9b51a8bfabc62d07"
was adding this checking

+       if (dev == FPGA_INVALID_DEVICE) {
+               puts("FPGA device not specified\n");
+               op = FPGA_NONE;
+       }

which simply broke one command flow which was
setenv fpga <dev>
fpga loadmk <addr> // legacy image
fpga loadmk <addr>:<fit_image_name> //fit image

Also this sequence for FIT image is completely broken
setenv fpga <dev>
setenv fpgadata <addr>:<fit_image_name>
fpga loadmk
(Note: For legacy images this is working fine).

even from code I don't think this has ever worked properly
for fit image (dev = FPGA_INVALID_DEVICE should be rejected
by fpga core). Fit image support was in 2008 added by:
"[new uImage] Add new uImage fromat support to fpga command"
(sha1: c28c4d193dbfb20b2dd3a5447640fd6de7fd0720)

Just a summary of these facts that none found this for pretty long time
it shouldn't be a problem to remove this flow (without fpga dev)
completely to simplify the code.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>