Platform: OLPC: move debugfs support from x86 EC driver

There's nothing about the debugfs interface for the EC driver that is
architecture-specific, so move it into the arch-independent driver.

The code is mostly unchanged with the exception of renamed variables, coding
style changes, and API updates.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Acked-by: Paul Fox <pgf@laptop.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>