omap3: Use raw SPL by default for mmc1

Now that we fall back to the FS code path when we don't find u-boot
at the raw sector offset, there is no good reason to not default to
raw boot.

With this patch, I can successfully boot u-boot from a raw sector
offset on beagle-xm.

Signed-off-by: Alexander Graf <agraf@suse.de>