mtd, ubi, ubifs: update for the sync with linux v3.14

while playing with the new mtd/ubi/ubifs sync, found some
small updates for it:

- add del_mtd_partition() to include/linux/mtd/mtd
- mtd: add a debug_printf
- remove some not used functions

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Tom Rini <trini@ti.com>