configs: sheevaplug: remove non-dm MMC driver

This will be replaced with the driver model version

Signed-off-by: Harm Berntsen <harm.berntsen@nedap.com>
Reviewed-by: Stefan Roese <sr@denx.de>
CC: Prafulla Wadaskar <prafulla@marvell.com>
CC: Stefan Roese <sr@denx.de>
CC: Tom Rini <trini@konsulko.com>