configs: remove unused CONFIG_SYS_MMC_BASE defs

These boards use an MMC driver that does not use this definition

Signed-off-by: Harm Berntsen <harm.berntsen@nedap.com>
Reviewed-by: Stefan Roese <sr@denx.de>
CC: Stefan Roese <sr@denx.de>
CC: Mario Six <mario.six@gdsys.cc>
CC: Dennis Gilmore <dgilmore@redhat.com>