drivers/platform/olpc/olpc-ec.c: initialise earlier

Being a low-level component, various drivers (e.g.  olpc-battery) assume
that it is ok to communicate with the OLPC Embedded Controller during
probe.  Therefore the OLPC EC driver must be initialised before other
drivers try to use it.  This was the case until it was recently moved
out of arch/x86 and restructured around commits ac250415 ("Platform:
OLPC: turn EC driver into a platform_driver") and 85f90cf6 ("x86:
OLPC: switch over to using new EC driver on x86").

Use arch_initcall so that olpc-ec is readied earlier, matching the
previous behaviour.

Fixes a regression introduced in Linux-3.6 where various drivers such as
olpc-battery and olpc-xo1-sci failed to load due to an inability to
communicate with the EC.  The user-visible effect was a lack of battery
monitoring, missing ebook/lid switch input devices, etc.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Cc: Andres Salomon <dilinger@queued.net>
Cc: Paul Fox <pgf@laptop.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>