configs: remove MTD support from bcm11130 and M54418TWR defconfigs

While the right Kconfig entries were selected, because of the missing
CMD_NAND symbol the raw NAND core was never compiled. Remove it from
the defconfigs otherwise the build will fail.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
[trini: Also do this on bcm11130_nand]
Signed-off-by: Tom Rini <trini@konsulko.com>