cmd: bcb: rework the command to U_BOOT_LONGHELP approach

cmd: bcb: rework the command to U_BOOT_LONGHELP approach

U_BOOT_LONGHELP and U_BOOT_CMD_WITH_SUBCMDS offer numerous advantages,
including:
- common argument restrictions checking
- automatic subcommand matching
- improved usage and help handling

By utilizing the U_BOOT_LONGHELP approach, we can reduce the amount of
command management code and describe commands more succinctly.

Signed-off-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> # vim3_android
Link: https://lore.kernel.org/r/20241017-android_ab_master-v5-2-43bfcc096d95@salutedevices.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>