x86, olpc: Add XO-1.5 SCI driver

Add a driver for the ACPI-based EC event interface found on the
OLPC XO-1.5 laptop. This enables notification of battery/AC power events,
and enables various devices to be used as wakeup sources through regular
ACPI mechanisms.

This driver can't be built as a module, because some drivers need to know
at boot-time if SCI-based functionality is available via
olpc_ec_wakeup_available().

Signed-off-by: Daniel Drake <dsd@laptop.org>
Link: http://lkml.kernel.org/r/1309019658-1712-12-git-send-email-dsd@laptop.org
Acked-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>