x86, olpc: Add missing Kconfig dependencies

OLPC uses select for OLPC_OPENFIRMWARE, which means OLPC has to
enforce the dependencies for OLPC_OPENFIRMWARE.  Make sure it does so.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Daniel Drake <dsd@laptop.org>
Cc: Andres Salomon <dilinger@queued.net>
Cc: Grant Likely <grant.likely@secretlab.ca>
LKML-Reference: <20100923162846.D8D409D401B@zog.reactivated.net>
Cc: <stable@kernel.org> 2.6.37