MIPS: defconfigs: add MTD_SPI_NOR (new dependency for M25P80)

MIPS: defconfigs: add MTD_SPI_NOR (new dependency for M25P80)

These defconfigs contain the CONFIG_M25P80 symbol, which is now
dependent on the MTD_SPI_NOR symbol. Add CONFIG_MTD_SPI_NOR to satisfy
the new dependency.

At the same time, drop the now-nonexistent CONFIG_MTD_CHAR symbol.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Huang Shijie <b32955@freescale.com>
Cc: Marek Vasut <marex@denx.de>
Cc: linux-mtd@lists.infradead.org
Patchwork: https://patchwork.linux-mips.org/patch/6878/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>