md: mem_dump() care all address cases

mem_dump() was used to dump multi length memory,
and it didn't care about 1 length dump.
Thus, cmd() implementation was unreadable.
This patch fixup mem_dump() to care all address cases.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
md: add -v option

-v : it ignore offset line print

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
md: add -V option

-V : it ignore address column print

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>