sh: Replace CONFIG_MTD_M25P80 with CONFIG_MTD_SPI_NOR in sh7757lcr_defconfig

CONFIG_MTD_M25P80 was removed and replaced by CONFIG_MTD_SPI_NOR 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: Rich Felker <dalias@libc.org>