MAINTAINERS: Add drivers/platform/olpc to drivers/platform/x86

Andy Shevchenko sent me a simple patch that's been sitting on LKML for
10 months for OLPC and asked if I'd take it via platform/drivers/x86.
OLPC appears to be unmaintained per MAINTAINERS. Add it to
platform/drivers/x86 (unless someone else really wants it!)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>