Platform: OLPC: turn EC driver into a platform_driver

The 1.75-based OLPC EC driver already does this; let's do it for all EC
drivers.  This gives us nice suspend/resume hooks, amongst other things.

We want to run the EC's suspend hooks later than other drivers (which may
be setting wakeup masks or be running EC commands).  We also want to run
the EC's resume hooks earlier than other drivers (which may want to run EC
commands).

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