arm/km: disable ls (through jffs2 support)

arm/km: disable ls (through jffs2 support)

This is not supported on our km-arm boards since we have defined
CONFIG_SYS_NO_FLASH for our NAND Flash chip.

With CONFIG_CMD_JFFS2, the ls command is present and works very badly
on our km-arm boards.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Acked-by: Heiko Schocher <hs@denx.de>
Acked-by: Prafulla Wadaskar <prafulla@marvell.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>