[MIPS] Add MTD device support for Cobalt

This patch has added MTD device support for Cobalt.
Moreover, removes old type FlashROM support.

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
5 files changed