common: command: Handle USAGE failure separately

common: command: Handle USAGE failure separately

command_ret_t enum contains 3 return values but only two are handled
now. Extend cmd_process_error() and handle CMD_RET_USAGE separately.

These commands are affected by this change.
cmd/demo.c
cmd/efi.c
cmd/gpio.c
cmd/qfw.c
cmd/x86/fsp.c
test/dm/cmd_dm.c

And scripts shouldn't be affected because return value is not 0. But
every command implementation can choose what it is correct to pass.
I would expect that RET_USAGE is called when parameters are not
correctly passed (have incorrect value, missing parameters)
and RET_FAILURE when correct parameters are passed but command fails.

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