cmd: Make use of U_BOOT_LONGHELP when missing

After adding the U_BOOT_LONGHELP macro some new commands came in still
that were not making use if it. Switch these cases over and in a few
places add missing newlines as well.

Signed-off-by: Tom Rini <trini@konsulko.com>
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Cc: Michal Simek <monstr@monstr.eu>

Changes in v2:
- Add the instances Michal noted I missed before