ARM: OMAP1: add MMC configuration for Palm Tungsten E

Add initial MMC configuration for Palm Tungsten E to allow using a proper
rootfs on the device. This still assumes the bootloader enabling the MMC,
and that the card is always present and writeable.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>