ARM: OMAP2+: n900 needs MMC slot names for legacy user space

Let's pass the slot names in pdata like the legacy code does.
Once we have a generic DT binding for the slot names we can
switch to that.

Tested-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>