cmd: fpga: improve user feedback in case of bitstream load failure

cmd: fpga: improve user feedback in case of bitstream load failure

In cmd/fpga.c, change some `debug` calls to `log_err` for important
user feedback and use CMD_RET_FAILURE in favor of CMD_RET_USAGE due to
its long output which hides the actual, useful return message. Change
the remaining `debug` calls to `log_debug`. Remove all 'fpga:' and
__func__ strings as log_* has this covered.

For `do_fpga_loads`, move up the `do_fpga_check_params` call for more
consistent command output; use a constant instead of multiple '5' use.

In drivers/fpga/zynq*.c, change 'up to' to 'above' which corrects this
confusing/wrong statement.

Signed-off-by: Pieter Van Trappen <pieter.van.trappen@cern.ch>
Link: https://lore.kernel.org/r/20250708152455.1214487-2-vtpieter@gmail.com
Signed-off-by: Michal Simek <michal.simek@amd.com>