The partitions parameter allows to partition a mtd device
using a standard cmdline partition description string. This
way the partitions of a mtd device can be changed at once.
The output of the string can be used to be passed to the kernel
as cmdline partition string. The partitions can also still be
changed with addpart/delpart, the partitions parameter will
be updated accordingly.

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