libmtd: rename functions from mtd_* to libmtd_* ...

The kernel nowadays has mtd_read/write and other functions. In
barebox we also have these functions, but with a different prototype,
namely they correspond to the libmtd userspace functions. Rename
these functions to libmtd_* to avoid name clashes with future mtd
updates.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

lib: add barebox version of libmtd ...

Based on mtd-utils and stripped down to needed functionality and
reworked to barebox interfaces.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>