There doesn't seem to be any good reason for all of the memory
commands (md, mw, etc.) to rely on a shared pre-allocated buffer
anymore. So, to simplify things, drop the shared buffer and adjust all
of the utilites to allocate needed memory.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>