With CONFIG_PARTITION_NEED_MTD enabled we use mtd rather than devfs
directly to create partitions on mtd devices. Since:

| commit b32cd8d
| Author: Sascha Hauer <s.hauer@pengutronix.de>
| Date:   Wed Apr 9 15:49:32 2014 +0200
|
|     mtd: nand: bb: use mtd api directly
|
|     The devfs layer just adds an addition indirection between mtd
|     and the bb devices with no purpose. Drop it.
|
|     Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

The bad block aware device creation doesn't work if this option
is disabled. With this we remove CONFIG_PARTITION_NEED_MTD and always
use mtd partitions on mtd devices.

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