mips: Drop CONFIG_MTD_M25P80 in various defconfig files

Drop CONFIG_MTD_M25P80 that was removed in
commit b35b9a10 ("mtd: spi-nor: Move m25p80 code in spi-nor.c")

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>