x86, olpc: Add XO-1 SCI driver and power button control

x86, olpc: Add XO-1 SCI driver and power button control

The System Control Interrupt is used in the OLPC XO-1 to control various
features of the laptop. Add the driver base and the power button
functionality.

This driver can't be built as a module, because functionality added in
future patches means that some drivers need to know at boot-time whether
SCI-based functionality is available.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Link: http://lkml.kernel.org/r/1309019658-1712-6-git-send-email-dsd@laptop.org
Acked-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>