x86, olpc: add debugfs interface for EC commands

x86, olpc: add debugfs interface for EC commands

Add a debugfs interface for sending commands to the OLPC Embedded
Controller (EC) and reading the responses.  The EC provides functionality
for machine identification, battery and AC control, wakeup control, etc.

Having a debugfs interface available is useful for EC development and
debugging.

Based on code by Paul Fox.

Signed-off-by: Paul Fox <pgf@laptop.org>
Signed-off-by: Daniel Drake <dsd@laptop.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andres Salomon <dilinger@queued.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>