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.