boards: mpfs_icicle: default to SPI_NOR_SFDP_RUNTIME

Default to SPI_NOR_SFDP_RUNTIME for the board so that it can build the
spi-nor driver without triggering the build check for:

jedec,spi-nor jedec-id required for non-runtime SFDP

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>